Regulation of endogenous gene expression in cells using zinc finger proteins

ABSTRACT

The present invention provides methods for modulating expression of endogenous cellular genes using recombinant zinc finger proteins.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/297,197, filed Jun. 5, 2014, which is a continuation of U.S.patent application Ser. No. 13/068,877, filed May 23, 2011, nowabandoned, which is a continuation of U.S. patent application Ser. No.10/984,304, filed Nov. 9, 2004, now abandoned, which is a continuationof U.S. patent application Ser. No. 09/897,844, filed Jul. 2, 2001, nowU.S. Pat. No. 6,979,539, issued Dec. 27, 2005, which is a continuationof U.S. patent application Ser. No. 09/229,037, filed Jan. 12, 1999, nowU.S. Pat. No. 6,534,261, issued Mar. 18, 2003. The present applicationclaims priority under 35 U.S.C. §120 to all of the aforementionedapplications, the disclosures of which are hereby incorporated byreference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with government support under Grant No. 1 R43DK52251-01, awarded by the National Institutes of Health. The governmenthas certain rights in this invention.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has beensubmitted electronically in ASCII format and is hereby incorporated byreference in its entirety. Said ASCII copy, created on Apr. 27, 2017, isnamed 8325000215_SL.txt and is 23,207 bytes in size.

FIELD OF THE INVENTION

The present invention provides methods for regulating gene expression ofendogenous genes using recombinant zinc finger proteins.

BACKGROUND OF THE INVENTION

Many, perhaps most physiological and pathophysiological processes can becontrolled by the selective up or down regulation of gene expression. Ifmethods existed for gene expression control, pathologies could betreated. Examples include the inappropriate expression of proinflamatorycytokines in rheumatoid arthritis, under expression of the hepatic LDLreceptor in hypercholesteremia, over expression of proangiogenic factorsand under expression of antiangiogenic factors in solid tumor growth, toname just a few. In addition, pathogenic organisms such as viruses,bacteria, fungi, and protozoa could be controlled by altering geneexpression. There is a clear unmet need for therapeutic approaches thatare simply able to up-regulate beneficial genes and down-regulatedisease causing genes.

In addition to the direct therapeutic utility provided by the ability tomanipulate gene expression, this ability can be used experimentally todetermine the function of a gene of interest. One common existing methodfor experimentally determining the function of a newly discovered geneis to clone its cDNA into an expression vector driven by a strongpromoter and measure the physiological consequence of itsover-expression in a transfected cell. This method is labor intensiveand does not address the physiological consequences of down-regulationof a target gene. Simple methods allowing the selective over andunder-expression of uncharacterized genes would be of great utility tothe scientific community. Methods that permit the regulation of genes incell model systems, transgenic animals and transgenic plants would findwidespread use in academic laboratories, pharmaceutical companies,genomics companies and in the biotechnology industry.

An additional use of tools permitting the manipulation of geneexpression is in the production of commercially useful biologicalproducts. Cell lines, transgenic animals and transgenic plants could beengineered to over-express a useful protein product. The production oferythropoietin by such an engineered cell line serves as an example.Likewise, production from metabolic pathways might be altered orimproved by the selective up or down-regulation of a gene encoding acrucial enzyme. An example of this is the production of plants withaltered levels of fatty acid saturation.

Methods currently exist in the art, which allow one to alter theexpression of a given gene, e.g., using ribozymes, antisense technology,small molecule regulators, over-expression of cDNA clones, andgene-knockouts. These methods have to date proven to be generallyinsufficient for many applications and typically have not demonstratedeither high target efficacy or high specificity in vivo. For usefulexperimental results and therapeutic treatments, these characteristicsare desired.

Gene expression is normally controlled through alterations in thefunction of sequence specific DNA binding proteins called transcriptionfactors. These bind in the general proximity (although occasionally atgreat distances) of the point of transcription initiation of a gene.They act to influence the efficiency of formation or function of atranscription initiation complex at the promoter. Transcription factorscan act in a positive fashion (transactivation) or in a negative fashion(transrepression).

Transcription factor function can be constitutive (always “on”) orconditional. Conditional function can be imparted on a transcriptionfactor by a variety of means, but the majority of these regulatorymechanisms depend of the sequestering of the factor in the cytoplasm andthe inducible release and subsequent nuclear translocation, DNA bindingand transactivation (or repression). Examples of transcription factorsthat function this way include progesterone receptors, sterol responseelement binding proteins (SREBPs) and NF-kappa B. There are examples oftranscription factors that respond to phosphorylation or small moleculeligands by altering their ability to bind their cognate DNA recognitionsequence (Hou et al., Science 256:1701 (1994); Gossen & Bujard, PNAS89:5547 (1992); Oligino et al., Gene Ther. 5:491-496 (1998); Wang etal., Gene Ther. 4:432-441 (1997); Neering et al., Blood 88:1147-1155(1996); and Rendahl et al., Nat. Biotechnol. 16:757-761 (1998)). Thismechanism is common in prokaryotes but somewhat less common ineukaryotes.

Zinc finger proteins (“ZFPs”) are proteins that can bind to DNA in asequence-specific manner. Zinc fingers were first identified in thetranscription factor TFIIIA from the oocytes of the African clawed toad,Xenopus laevis. ZFPs are widespread in eukaryotic cells. An exemplarymotif characterizing one class of these proteins (C₂H₂ class) is-Cys-(X)₂₋₄-Cys-(X)₁₂-His-(X)₃₋₅-His (where X is any amino acid). Asingle finger domain is about 30 amino acids in length and severalstructural studies have demonstrated that it contains an alpha helixcontaining the two invariant histidine residues co-ordinated throughzinc with the two cysteines of a single beta turn. To date, over 10,000zinc finger sequences have been identified in several thousand known orputative transcription factors. ZFPs are involved not only inDNA-recognition, but also in RNA binding and protein-protein binding.Current estimates are that this class of molecules will constitute about2% of all human genes.

The X-ray crystal structure of Zif268, a three-finger domain from amurine transcription factor, has been solved in complex with its cognateDNA-sequence and shows that each finger can be superimposed on the nextby a periodic rotation and translation of the finger along the main DNAaxis. The structure suggests that each finger interacts independentlywith DNA over 3 base-pair intervals, with side-chains at positions −1,2, 3 and 6 on each recognition helix making contacts with respective DNAtriplet sub-site. The amino terminus of Zif268 is situated at the 3′ endof its DNA recognition subsite. Recent results have indicated that somezinc fingers can bind to a fourth base in a target segment (Isalan etal., PNAS 94:5617-5621 (1997). The fourth base is on the opposite strandfrom the other three bases recognized by zinc finger and complementaryto the base immediately 3′ of the three base subsite.

The structure of the Zif268-DNA complex also suggested that the DNAsequence specificity of a ZFP might be altered by making amino acidsubstitutions at the four helix positions (−1, 2, 3 and 6) on a zincfinger recognition helix. Phage display experiments using zinc fingercombinatorial libraries to test this observation were published in aseries of papers in 1994 (Rebar et al., Science 263:671-673 (1994);Jamieson et al., Biochemistry 33:5689-5695 (1994); Choo et al., PNAS91:11163-11167 (1994)). Combinatorial libraries were constructed withrandomized side-chains in either the first or middle finger of Zif268and then isolated with an altered Zif268 binding site in which theappropriate DNA sub-site was replaced by an altered DNA triplet.Correlation between the nature of introduced mutations and the resultingalteration in binding specificity gave rise to a partial set ofsubstitution rules for rational design of ZFPs with altered bindingspecificity.

Greisman & Pabo, Science 275:657-661 (1997) discuss an elaboration of aphage display method in which each finger of a zinc finger protein issuccessively subjected to randomization and selection. This paperreported selection of ZFPs for a nuclear hormone response element, a p53target site and a TATA box sequence.

Recombinant ZFPs have been reported to have the ability to regulate geneexpression of transiently expressed reporter genes in cultured cells(see, e.g., Pomerantz et al., Science 267:93-96 (1995); Liu et al., PNAS94:5525-5530 1997); and Beerli et al., PNAS 95:14628-14633 (1998)).

For example, Pomerantz et al., Science 267:93-96 (1995) report anattempt to design a novel DNA binding protein by fusing two fingers fromZif268 with a homeodomain from Oct-1. The hybrid protein was then fusedwith either a transcriptional activator or repressor domain forexpression as a chimeric protein. The chimeric protein was reported tobind a target site representing a hybrid of the subsites of its twocomponents. The authors then constructed a reporter vector containing aluciferase gene operably linked to a promoter and a hybrid site for thechimeric DNA binding protein in proximity to the promoter. The authorsreported that their chimeric DNA binding protein could activate orrepress expression of the luciferase gene.

Liu et al., PNAS 94:5525-5530 (1997) report forming a composite ZFP byusing a peptide spacer to link two component ZFPs, each having threefingers. The composite protein was then further linked totranscriptional activation or repression domains. It was reported thatthe resulting chimeric protein bound to a target site formed from thetarget segments bound by the two component ZFPs. It was further reportedthat the chimeric ZFP could activate or repress transcription of areporter gene when its target site was inserted into a reporter plasmidin proximity to a promoter operably linked to the reporter.

Beerli et al., PNAS 95:14628-14633 (1998) report construction of achimeric six finger ZFP fused to either a KRAB, ERD, or SIDtranscriptional repressor domain, or the VP16 or VP64 transcriptionalactivation domain. This chimeric ZFP was designed to recognize an 18 bptarget site in the 5′ untranslated region of the human erbB-2 gene.Using this construct, the authors of this study report both activationand repression of a transiently expressed reporter luciferase constructlinked to the erbB-2 promoter.

In addition, a recombinant ZFP was reported to repress expression of anintegrated plasmid construct encoding a bcr-abl oncogene (Choo et al.,Nature 372:642-645 (1994)). The target segment to which the ZFPs boundwas a nine base sequence GCA GAA GCC chosen to overlap the junctioncreated by a specific oncogenic translocation fusing the genes encodingbcr and abl. The intention was that a ZFP specific to this target sitewould bind to the oncogene without binding to abl or bcr componentgenes. The authors used phage display to select a variant ZFP that boundto this target segment. the variant ZFP thus isolated was then reportedto repress expression of a stably transfected bcr-abl construct in acell line.

To date, these methods have focused on regulation of either transientlyexpressed genes, or on regulation of exogenous genes that have beenintegrated into the genome. The transiently expressed genes described byPomerantz et al., Liu et al., and Beerli et al. are episomal and are notpackaged into chromatin in the same manner as chromosomal genes.Moreover, even the stably expressed gene described by Choo et al. israndomly integrated into the genome and is not found in a nativechromatin environment as compared to an endogenous gene. In contrast,specific regulation of an endogenous cellular gene in its nativechromatin environment using a ZFP has not yet been demonstrated in theart.

SUMMARY OF THE INVENTION

The present invention thus provides for the first time methods ofregulating endogenous cellular gene expression, where the endogenousgenes are in their native chromatin environment, in contrast to genesthat have been transiently expressed in a cell, or those that have beenexogenously integrated into the genome. In one preferred embodiment, themethods of regulation use ZFPs with a K_(d) of less than about 25 nM toactivate or repress gene transcription. The ZFPs of the inventiontherefore can be used to repress transcription of an endogenous cellulargene by 20% or more, and can be used to activate transcription of anendogenous cellular gene by about 1.5 fold or more.

In one aspect, the present invention provides a method of inhibitingexpression of an endogenous cellular gene in a cell, the methodcomprising the step of: contacting a first target site in the endogenouscellular gene with a first zinc finger protein, wherein the K_(d) of thezinc finger protein is less than about 25 nM; thereby inhibitingexpression of the endogenous cellular gene by at least about 20%.

In another aspect, the present invention provides a method of inhibitingexpression of an endogenous cellular gene in a cell, the methodcomprising the step of: contacting a target site in the endogenouscellular gene with a fusion zinc finger protein comprising six fingersand a regulatory domain, wherein the K_(d) of the zinc finger protein isless than about 25 nM; thereby inhibiting expression of the endogenouscellular gene by at least about 20%.

In one embodiment, expression of the endogenous cellular gene isinhibited by at least about 75%-100%. In another embodiment, theinhibition of gene expression prevents gene activation.

In another aspect, the present invention provides a method of activatingexpression of an endogenous cellular gene, the method comprising thestep of: contacting a first target site in the endogenous cellular genewith a first zinc finger protein, wherein the K_(d) of the zinc fingerprotein is less than about 25 nM; thereby activating expression of theendogenous cellular gene to at least about 150%.

In another aspect, the present invention provides a method of activatingexpression of an endogenous cellular gene, the method comprising thestep of: contacting a target site in the endogenous cellular gene with afusion zinc finger protein comprising six fingers and a regulatorydomain, wherein the K_(d) of the zinc finger protein is less than about25 nM; thereby activating expression of the endogenous cellular gene toat least about 150%.

In one embodiment, expression of the endogenous cellular gene isactivated to at least about 200-500%. In another embodiment, activationof gene expression prevents repression of gene expression.

In another aspect, the present invention provides a method of modulatingexpression of an endogenous cellular gene in a cell, the methodcomprising the step of: contacting a first target site in the endogenouscellular gene with a first zinc finger protein; thereby modulatingexpression of the endogenous cellular gene.

In another aspect, the present invention provides a method of modulatingexpression of an endogenous cellular gene in a cell, the methodcomprising the step of: contacting a target site in the endogenouscellular gene with a fusion zinc finger protein comprising six fingersand a regulatory domain; thereby modulating expression of the endogenouscellular gene.

In one embodiment, the step of contacting further comprises contacting asecond target site in the endogenous cellular gene with a second zincfinger protein. In another embodiment, the first and second target sitesare adjacent. In another embodiment, the first and second zinc fingerproteins are covalently linked. In another embodiment, the first zincfinger protein is a fusion protein comprising a regulatory domain. Inanother embodiment, the first zinc finger protein is a fusion proteincomprising at least two regulatory domains. In another embodiment, thefirst and second zinc finger proteins are fusion proteins, eachcomprising a regulatory domain. In another embodiment, the first andsecond zinc finger protein are fusion proteins, each comprising at leasttwo regulatory domains.

In one embodiment, the endogenous cellular gene is a selected from thegroup consisting of VEGF, ERα, IGF-I, c-myc, c-myb, ICAM, Her2/Neu,FAD2-1, EPO, GM-CSF, GDNF, and LDL-R. In another embodiment, theregulatory domain is selected from the group consisting of atranscriptional repressor, a transcriptional activator, an endonuclease,a methyl transferase, a histone acetyltransferase, and a histonedeacetylase.

In one embodiment, the cell is selected from the group consisting ofanimal cell, a plant cell, a bacterial cell, a protozoal cell, or afungal cell. In another embodiment, the cell is a mammalian cell. Inanother embodiment, the cell is a human cell.

In one embodiment, the method further comprises the step of firstadministering to the cell a delivery vehicle comprising the zinc fingerprotein, wherein the delivery vehicle comprises a liposome or a membranetranslocation polypeptide.

In one embodiment, the zinc finger protein is encoded by a zinc fingerprotein nucleic acid operably linked to a promoter, and the methodfurther comprises the step of first administering the nucleic acid tothe cell in a lipid:nucleic acid complex or as naked nucleic acid. Inanother embodiment, the zinc finger protein is encoded by an expressionvector comprising a zinc finger protein nucleic acid operably linked toa promoter, and the method further comprises the step of firstadministering the expression vector to the cell. In another embodiment,the expression vector is a viral expression vector. In anotherembodiment, the expression vector is a retroviral expression vector, anadenoviral expression vector, a DNA plasmid expression vector, or an AAVexpression vector.

In one the zinc finger protein is encoded by a nucleic acid operablylinked to an inducible promoter. In another embodiment, the zinc fingerprotein is encoded by a nucleic acid operably linked to a weak promoter.

In one embodiment, the cell comprises less than about 1.5×10⁶ copies ofthe zinc finger protein.

In one embodiment, the target site is upstream of a transcriptioninitiation site of the endogenous cellular gene. In another embodiment,the target site is adjacent to a transcription initiation site of theendogenous cellular gene. In another embodiment, the target site isadjacent to an RNA polymerase pause site downstream of a transcriptioninitiation site of the endogenous cellular gene.

In another embodiment, the zinc finger protein comprises an SP-1backbone. In one embodiment, the zinc finger protein comprises aregulatory domain and is humanized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: PCR amplification scheme for production of ZFP-encodingsynthetic genes.

FIGS. 2A-2C. Expression and purification of typical ZFPs. FIG. 2A:Unfused ZFP before induction (lane 1), after induction (lane 2), andafter purification (lane 3). FIG. 2B: MBP-VEGF expression beforeinduction (lane 1), after induction (lane 2), and after French Presslysis (lane 3). FIG. 2C: Purification of MBP-VEGF by amylose affinitycolumn showing flow-through (FT), and initial fractions (1-4). Fraction2 was used for electrophoretic mobility shift assays (“EMSA”). M,molecular weight markers.

FIG. 3. Typical EMSA experiment with MBP fused ZFP. MBP-VEGF1 proteinwas bound to labeled duplex DNA as described in the text. A three-foldprotein dilution series was carried out; each point represents thepercent shifted at that particular protein concentration plotted on asemi-log graph. Quantitation was by phosphorimager. In this case, theprotein concentration yielding 50% of maximum shift (the apparent K_(d))was 2 nM.

FIGS. 4A-4B. Off-rate experiment comparing VEGF1 to VEGF3a/1. FIG. 4A:Protein-DNA complexes were pre-formed and incubated with a 1000-foldexcess of unlabeled oligonucleotide. Samples were electrophoresed atvarious times and the amount of shifted product was measured byphosphorimager. FIG. 4B: Curve fitting was used to calculate theindicated complex half-lives.

FIG. 5. Typical expression vector used for transient ZFP expression inmammalian cells.

FIG. 6. Co-transfection data showing repression of luciferase reporteractivity via VEGF-KRAB protein expression. Error bars show the standarddeviation of triplicate transfections. pGL3-C (reporter vector control);pVFR1-4x (VEGF reporter plasmid); VEGF1 (VEGF1-KRAB); VEGF3a(VEGF3a-KRAB); VEGF3a/1 (VEGF3a/1-KRAB).

FIG. 7. Co-transfection data showing activation of luciferase reporteractivity via VEGF-VP16 protein expression. Error bars show the standarddeviation of triplicate transfections. pGL3-P (reporter with no VEGFtarget); pcDNA (empty effector vector control); pVFR3-4x (VEGF reporterplasmid); VEGF1 (VEGF1-VP16); VEGF3a (VEGF3a-VP16); VEGF3a/1(VEGF3a/1-VP16).

FIG. 8. VEGF ELISA data showing repression of endogenous VEGF geneexpression due to transfection of a VEGF ZFP-KRAB effector plasmid. DFXtreated (control nontransfected Dfx treated cells; No ZFP(pcDNA-control), VEGF 1 (VEGF1-KRAB), VEGF 3a/1 (VEGF3a/1-KRAB), CCR5(CCR5-KRAB); Mock uninduced (mock transfected cells untreated with DFX).Error bars show the standard deviation of duplicate transfections.

FIG. 9. VEGF ELISA data showing activation of endogenous VEGF geneexpression due to transfection of a VEGF ZFP-VP16 effector plasmid. Mock(mock transfected cells); No ZFP (NVF-control), VEGF 1 (VEGF1-VP16),VEGF 3a/1 (VEGF3a/1-VP16). Error bars show the standard deviation ofduplicate transfections.

FIGS. 10A-10B. RNase protection assay showing changes in VEGF specificmRNA by VEGF-specific ZFPs. FIG. 10A: Activation of VEGF mRNA,NVF-Control (no ZFP), VEGF1-NVF (VEGF1-VP16), CCR5-5-NVF (CCR5-VP16),CCR5-3-NVF (CCR5-VP16). FIG. 10B: Repression of VEGF mRNA. NKF-Control(no ZFP), VEGF1-NKF (VEGF1-KRAB), VEGF3a/1-NKF (VEGF3a/1-KRAB),CCR5-3-NKF (CCR5-KRAB). The size of the 148 nucleotide VEGF specificband is indicated by an arrow. The VEGF specific probe was synthesizedfrom a human angiogenesis multi-probe template set (Pharmingen). As acontrol, signals from the housekeeping genes L32 and GAPDH are shown(arrrows).

DETAILED DESCRIPTION OF THE INVENTION Introduction

The present application demonstrates for the first time that ZFPs can beused to regulate expression of an endogenous cellular gene that ispresent in its native chromatin environment. The present invention thusprovides zinc finger DNA binding proteins that have been engineered tospecifically recognize, with high efficacy, endogenous cellular genes.The experiments described herein demonstrate that a 3 finger ZFP with atarget site affinity of less than about 10 nM (VEGF1) can be used toeffectively activate or repress activity of an endogenous gene.Furthermore, a 6 finger ZFP (VEGF3a/1) was also shown to effectivelyrepress activity of an endogenous gene. Preferably, the ZFPs of theinvention exhibit high affinity for their target sites, with K_(d)s ofless than about 100 nM, preferably less than about 50 nM, mostpreferably less than about 25 nM or lower.

As a result, the ZFPs of the invention can be used to regulateendogenous gene expression, both through activation and repression ofendogenous gene transcription. The ZFPs can also be linked to regulatorydomains, creating chimeric transcription factors to activate or represstranscription. In one preferred embodiment, the methods of regulationuse ZFPs with a K_(d) of less than about 25 nM to activate or repressgene transcription. The ZFPs of the invention therefore can be used torepress transcription of an endogenous cellular gene by 20% or more, andcan be used to activate transcription of an endogenous cellular gene byabout 1.5 fold or more.

Such methods of regulating gene expression allow for novel human andmammalian therapeutic applications, e.g., treatment of genetic diseases,cancer, fungal, protozoal, bacterial, and viral infection, ischemia,vascular disease, arthritis, immunological disorders, etc., as well asproviding means for functional genomics assays, and means for developingplants with altered phenotypes, including disease resistance, fruitripening, sugar and oil composition, yield, and color.

As described herein, ZFPs can be designed to recognize any suitabletarget site, for regulation of expression of any endogenous gene ofchoice. Examples of endogenous genes suitable for regulation includeVEGF, CCR5, ERα, Her2/Neu, Tat, Rev, HBV C, S, X, and P, LDL-R, PEPCK,CYP7, Fibrinogen, ApoB, Apo E, Apo(a), renin, NF-κB, I-κB, TNF-α, FASligand, amyloid precursor protein, atrial naturetic factor, ob-leptin,ucp-1, IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-12, G-CSF, GM-CSF, Epo,PDGF, PAF, p53, Rb, fetal hemoglobin, dystrophin, eutrophin, GDNF, NGF,IGF-1, VEGF receptors fit and flk, topoisomerase, telomerase, bcl-2,cyclins, angiostatin, IGF, ICAM-1, STATS, c-myc, c-myb, TH, PTI-1,polygalacturonase, EPSP synthase, FAD2-1, delta-12 desaturase, delta-9desaturase, delta-15 desaturase, acetyl-CoA carboxylase,acyl-ACP-thioesterase, ADP-glucose pyrophosphorylase, starch synthase,cellulose synthase, sucrose synthase, senescence-associated genes, heavymetal chelators, fatty acid hydroperoxide lyase, viral genes, protozoalgenes, fungal genes, and bacterial genes. In general, suitable genes tobe regulated include cytokines, lymphokines, growth factors, mitogenicfactors, chemotactic factors, onco-active factors, receptors, potassiumchannels, G-proteins, signal transduction molecules, and otherdisease-related genes.

A general theme in transcription factor function is that simple bindingand sufficient proximity to the promoter are all that is generallyneeded. Exact positioning relative to the promoter, orientation, andwithin limits, distance do not matter greatly. This feature allowsconsiderable flexibility in choosing sites for constructing artificialtranscription factors. The target site recognized by the ZFP thereforecan be any suitable site in the target gene that will allow activationor repression of gene expression by a ZFP, optionally linked to aregulatory domain. Preferred target sites include regions adjacent to,downstream, or upstream of the transcription start site. In addition,target sites that are located in enhancer regions, repressor sites, RNApolymerase pause sites, and specific regulatory sites (e.g., SP-1 sites,hypoxia response elements, nuclear receptor recognition elements, p53binding sites), sites in the cDNA encoding region or in an expressedsequence tag (EST) coding region. As described below, typically eachfinger recognizes 2-4 base pairs, with a two finger ZFP binding to a 4to 7 bp target site, a three finger ZFP binding to a 6 to 10 base pairsite, and a six finger ZFP binding to two adjacent target sites, eachtarget site having from 6-10 base pairs.

As described herein, two ZFPs can be administered to a cell, recognizingeither the same target endogenous cellular gene, or different targetendogenous cellular gene. The first ZFP optionally is associated withthe second ZFP, either covalently or non-covalently. Recognition ofadjacent target sites by either associated or individual ZFPs can beused to produce cooperative binding of the ZFPs, resulting in anaffinity that is greater than the affinity of the ZFPs when individuallybound to their target site.

In one embodiment, two ZFPs are produced as a fusion protein linked byan amino acid linker, and the resulting six finger ZFP recognizes anapproximately 18 base pair target site (see, e.g., Liu et al., PNAS94:5525-5530 (1997)). An 18 base pair target site is expected to providespecificity in the human genome, as a target site of that size shouldoccur only once in every 3×10¹⁰ base pairs, and the size of the humangenome is 3.5×10⁹ base pairs (see, e.g., Liu et al., PNAS 94:5525-5530(1997)). In another embodiment, the ZFPs are non-covalently associated,through a leucine zipper, a STAT protein N-terminal domain, or the FK506binding protein (see, e.g., O'Shea, Science 254: 539 (1991),Barahmand-Pour et al., Curr. Top. Microbiol. Immunol. 211:121-128(1996); Klemm et al., Annu. Rev. Immunol. 16:569-592 (1998); Ho et al.,Nature 382:822-826 (1996)).

In another embodiment, the ZFP is linked to at least one or moreregulatory domains, described below. Preferred regulatory domainsinclude transcription factor repressor or activator domains such as KRABand VP16, co-repressor and co-activator domains, DNA methyltransferases, histone acetyltransferases, histone deacetylases, andendonucleases such as Fok1. For repression of gene expression, typicallythe expression of the gene is reduced by about 20% (i.e., 80% of non-ZFPmodulated expression), more preferably by about 50% (i.e., 50% ofnon-ZFP modulated expression), more preferably by about 75-100% (i.e.,25% to 0% of non-ZFP modulated expression). For activation of geneexpression, typically expression is activated by about 1.5 fold (i.e.,150% of non-ZFP modulated expression), preferably 2 fold (i.e., 200% ofnon-ZFP modulated expression), more preferably 5-10 fold (i.e.,500-1000% of non-ZFP modulated expression), up to at least 100 fold ormore.

The expression of engineered ZFP activators and repressors can be alsocontrolled by systems typified by the tet-regulated systems and theRU-486 system (see, e.g., Gossen & Bujard, PNAS 89:5547 (1992); Oliginoet al., Gene Ther. 5:491-496 (1998); Wang et al., Gene Ther. 4:432-441(1997); Neering et al., Blood 88:1147-1155 (1996); and Rendahl et al.,Nat. Biotechnol. 16:757-761 (1998)). These impart small molecule controlon the expression of the ZFP activators and repressors and thus impartsmall molecule control on the target gene(s) of interest. Thisbeneficial feature could be used in cell culture models, in genetherapy, and in transgenic animals and plants.

Definitions

As used herein, the following terms have the meanings ascribed to themunless specified otherwise.

The term “zinc finger protein” or “ZFP” refers to a protein having DNAbinding domains that are stabilized by zinc. The individual DNA bindingdomains are typically referred to as “fingers” A ZFP has least onefinger, typically two fingers, three fingers, or six fingers. Eachfinger binds from two to four base pairs of DNA, typically three or fourbase pairs of DNA. A ZFP binds to a nucleic acid sequence called atarget site or target segment. Each finger typically comprises anapproximately 30 amino acid, zinc-chelating, DNA-binding subdomain. Anexemplary motif characterizing one class of these proteins (C₂H₂ class)is -Cys-(X)₂₋₄-Cys-(X)₁₂-His-(X)₃₋₅-His (where X is any amino acid).Studies have demonstrated that a single zinc finger of this classconsists of an alpha helix containing the two invariant histidineresidues co-ordinated with zinc along with the two cysteine residues ofa single beta turn (see, e.g., Berg & Shi, Science 271:1081-1085(1996)).

A “target site” is the nucleic acid sequence recognized by a ZFP. Asingle target site typically has about four to about ten base pairs.Typically, a two-fingered ZFP recognizes a four to seven base pairtarget site, a three-fingered ZFP recognizes a six to ten base pairtarget site, and a six fingered ZFP recognizes two adjacent nine to tenbase pair target sites.

The term “adjacent target sites” refers to non-overlapping target sitesthat are separated by zero to about 5 base pairs.

“K_(d)” refers to the dissociation constant for the compound, i.e., theconcentration of a compound (e.g., a zinc finger protein) that giveshalf maximal binding of the compound to its target (i.e., half of thecompound molecules are bound to the target) under given conditions(i.e., when [target]<<K_(d)), as measured using a given assay system(see, e.g., U.S. Pat. No. 5,789,538). The assay system used to measurethe K_(d) should be chosen so that it gives the most accurate measure ofthe actual K_(d) of the ZFP. Any assay system can be used, as long is itgives an accurate measurement of the actual K_(d) of the ZFP. In oneembodiment, the K_(d) for the ZFPs of the invention is measured using anelectrophoretic mobility shift assay (“EMSA”), as described in Example Iand on page 14 of the present specification. Unless an adjustment ismade for ZFP purity or activity, the K_(d) calculations made using themethod of Example I may result in an underestimate of the true K_(d) ofa given ZFP. Preferably, the K_(d) of a ZFP used to modulatetranscription of an endogenous cellular gene is less than about 100 nM,more preferably less than about 75 nM, more preferably less than about50 nM, most preferably less than about 25 nM.

An “endogenous cellular gene” refers to a gene that is native to a cell,which is in its normal genomic and chromatin context, and which is notheterologous to the cell. Such cellular genes include, e.g., animalgenes, plant genes, bacterial genes, protozoal genes, fungal genes,mitrochondrial genes, and chloroplastic genes.

An “endogenous gene” refers to a microbial or viral gene that is part ofa naturally occurring microbial or viral genome in a microbially orvirally infected cell. The microbial or viral genome can beextrachromosomal or integrated into the host chromosome. This term alsoencompasses endogenous cellular genes, as described above.

A “native chromatin environment” refers to the naturally occurring,structural relationship of genomic DNA (e.g., bacterial, animal, fungal,plant, protozoal, mitochondrial, and chloroplastic) and DNA-bindingproteins (e.g., histones and bacterial DNA binding protein II), whichtogether form chromosomes. The endogenous cellular gene can be in atranscriptionally active or inactive state in the native chromatinenvironment.

The phrase “adjacent to a transcription initiation site” refers to atarget site that is within about 50 bases either upstream or downstreamof a transcription initiation site. “Upstream” of a transcriptioninitiation site refers to a target site that is more than about 50 bases5′ of the transcription initiation site (i.e., in the non-transcribedregion of the gene).

The phrase “RNA polymerase pause site” is described in Uptain et al.,Annu. Rev. Biochem. 66:117-172 (1997).

“Humanized” refers to a non-human polypeptide sequence that has beenmodified to minimize immunoreactivity in humans, typically by alteringthe amino acid sequence to mimic existing human sequences, withoutsubstantially altering the function of the polypeptide sequence (see,e.g., Jones et al., Nature 321:522-525 (1986), and published UK patentapplication No. 8707252). Backbone sequences for the ZFPs are preferablybe selected from existing human C₂H₂ ZFPs (e.g., SP-1). Functionaldomains are preferably selected from existing human genes, (e.g., theactivation domain from the p65 subunit of NF-κB). Where possible, therecognition helix sequences will be selected from the thousands ofexisting ZFP DNA recognition domains provided by sequencing the humangenome. As much as possible, domains will be combined as units from thesame existing proteins. All of these steps will minimize theintroduction of new junctional epitopes in the chimeric ZFPs and renderthe engineered ZFPs less immunogenic.

“Administering” an expression vector, nucleic acid, ZFP, or a deliveryvehicle to a cell comprises transducing, transfecting, electroporating,translocating, fusing, phagocytosing, shooting or ballistic methods,etc., i.e., any means by which a protein or nucleic acid can betransported across a cell membrane and preferably into the nucleus of acell.

A “delivery vehicle” refers to a compound, e.g., a liposome, toxin, or amembrane translocation polypeptide, which is used to administer a ZFP.Delivery vehicles can also be used to administer nucleic acids encodingZFPs, e.g., a lipid:nucleic acid complex, an expression vector, a virus,and the like.

The terms “modulating expression” “inhibiting expression” and“activating expression” of a gene refer to the ability of a ZFP toactivate or inhibit transcription of a gene. Activation includesprevention of transcriptional inhibition (i.e., prevention of repressionof gene expression) and inhibition includes prevention oftranscriptional activation (i.e., prevention of gene activation).

Modulation can be assayed by determining any parameter that isindirectly or directly affected by the expression of the target gene.Such parameters include, e.g., changes in RNA or protein levels, changesin protein activity, changes in product levels, changes in downstreamgene expression, changes in reporter gene transcription (luciferase,CAT, β-galactosidase, β-glucuronidase, GFP (see, e.g., Mistili &Spector, Nature Biotechnology 15:961-964 (1997)); changes in signaltransduction, phosphorylation and dephosphorylation, receptor-ligandinteractions, second messenger concentrations (e.g., cGMP, cAMP, IP3,and Ca²⁺), cell growth, and neovascularization. These assays can be invitro, in vivo, and ex vivo. Such functional effects can be measured byany means known to those skilled in the art, e.g., measurement of RNA orprotein levels, measurement of RNA stability, identification ofdownstream or reporter gene expression, e.g., via chemiluminescence,fluorescence, colorimetric reactions, antibody binding, induciblemarkers, ligand binding assays; changes in intracellular secondmessengers such as cGMP and inositol triphosphate (IP3); changes inintracellular calcium levels; cytokine release, and the like.

To determine the level of gene expression modulation by a ZFP, cellscontacted with ZFPs are compared to control cells, e.g., without thezinc finger protein or with a non-specific ZFP, to examine the extent ofinhibition or activation. Control samples are assigned a relative geneexpression activity value of 100%. Modulation/inhibition of geneexpression is achieved when the gene expression activity value relativeto the control is about 80%, preferably 50% (i.e., 0.5× the activity ofthe control), more preferably 25%, more preferably 5-0%.Modulation/activation of gene expression is achieved when the geneexpression activity value relative to the control is 110%, morepreferably 150% (i.e., 1.5x the activity of the control), morepreferably 200-500%, more preferably 1000-2000% or more.

A “transcriptional activator” and a “transcriptional repressor” refer toproteins or effector domains of proteins that have the ability tomodulate transcription, as described above. Such proteins include, e.g.,transcription factors and co-factors (e.g., KRAB, MAD, ERD, SID, nuclearfactor kappa B subunit p65, early growth response factor 1, and nuclearhormone receptors, VP16, VP64), endonucleases, integrases, recombinases,methyltransferases, histone acetyltransferases, histone deacetylasesetc. Activators and repressors include co-activators and co-repressors(see, e.g., Utley et al., Nature 394:498-502 (1998)).

A “regulatory domain” refers to a protein or a protein domain that hastranscriptional modulation activity when tethered to a DNA bindingdomain, i.e., a ZFP. Typically, a regulatory domain is covalently ornon-covalently linked to a ZFP to effect transcription modulation.Alternatively, a ZFP can act alone, without a regulatory domain, toeffect transcription modulation.

The term “heterologous” is a relative term, which when used withreference to portions of a nucleic acid indicates that the nucleic acidcomprises two or more subsequences that are not found in the samerelationship to each other in nature. For instance, a nucleic acid thatis recombinantly produced typically has two or more sequences fromunrelated genes synthetically arranged to make a new functional nucleicacid, e.g., a promoter from one source and a coding region from anothersource. The two nucleic acids are thus heterologous to each other inthis context. When added to a cell, the recombinant nucleic acids wouldalso be heterologous to the endogenous genes of the cell. Thus, in achromosome, a heterologous nucleic acid would include an non-native(non-naturally occurring) nucleic acid that has integrated into thechromosome, or a non-native (non-naturally occurring) extrachromosomalnucleic acid. In contrast, a naturally translocated piece of chromosomewould not be considered heterologous in the context of this patentapplication, as it comprises an endogenous nucleic acid sequence that isnative to the mutated cell.

Similarly, a heterologous protein indicates that the protein comprisestwo or more subsequences that are not found in the same relationship toeach other in nature (e.g., a “fusion protein,” where the twosubsequences are encoded by a single nucleic acid sequence). See, e.g.,Ausubel, supra, for an introduction to recombinant techniques.

The term “recombinant” when used with reference, e.g., to a cell, ornucleic acid, protein, or vector, indicates that the cell, nucleic acid,protein or vector, has been modified by the introduction of aheterologous nucleic acid or protein or the alteration of a nativenucleic acid or protein, or that the cell is derived from a cell somodified. Thus, for example, recombinant cells express genes that arenot found within the native (naturally occurring) form of the cell orexpress a second copy of a native gene that is otherwise normally orabnormally expressed, under expressed or not expressed at all.

A “promoter” is defined as an array of nucleic acid control sequencesthat direct transcription. As used herein, a promoter typically includesnecessary nucleic acid sequences near the start site of transcription,such as, in the case of certain RNA polymerase II type promoters, a TATAelement, enhancer, CCAAT box, SP-1 site, etc. As used herein, a promoteralso optionally includes distal enhancer or repressor elements, whichcan be located as much as several thousand base pairs from the startsite of transcription. The promoters often have an element that isresponsive to transactivation by a DNA-binding moiety such as apolypeptide, e.g., a nuclear receptor, Gal4, the lac repressor and thelike.

A “constitutive” promoter is a promoter that is active under mostenvironmental and developmental conditions. An “inducible” promoter is apromoter that is active under certain environmental or developmentalconditions.

A “weak promoter” refers to a promoter having about the same activity asa wild type herpes simplex virus (“HSV”) thymidine kinase (“tk”)promoter or a mutated HSV tk promoter, as described in Eisenberg &McKnight, Mol. Cell. Biol. 5:1940-1947 (1985).

The term “operably linked” refers to a functional linkage between anucleic acid expression control sequence (such as a promoter, or arrayof transcription factor binding sites) and a second nucleic acidsequence, wherein the expression control sequence directs transcriptionof the nucleic acid corresponding to the second sequence.

An “expression vector” is a nucleic acid construct, generatedrecombinantly or synthetically, with a series of specified nucleic acidelements that permit transcription of a particular nucleic acid in ahost cell, and optionally integration or replication of the expressionvector in a host cell. The expression vector can be part of a plasmid,virus, or nucleic acid fragment, of viral or non-viral origin.Typically, the expression vector includes an “expression cassette,”which comprises a nucleic acid to be transcribed operably linked to apromoter. The term expression vector also encompasses naked DNA operablylinked to a promoter.

By “host cell” is meant a cell that contains a ZFP or an expressionvector or nucleic acid encoding a ZFP. The host cell typically supportsthe replication or expression of the expression vector. Host cells maybe prokaryotic cells such as E. coli, or eukaryotic cells such as yeast,fungal, protozoal, higher plant, insect, or amphibian cells, ormammalian cells such as CHO, HeLa, 293, COS-1, and the like, e.g.,cultured cells (in vitro), explants and primary cultures (in vitro andex vivo), and cells in vivo.

“Nucleic acid” refers to deoxyribonucleotides or ribonucleotides andpolymers thereof in either single- or double-stranded form. The termencompasses nucleic acids containing known nucleotide analogs ormodified backbone residues or linkages, which are synthetic, naturallyoccurring, and non-naturally occurring, which have similar bindingproperties as the reference nucleic acid, and which are metabolized in amanner similar to the reference nucleotides. Examples of such analogsinclude, without limitation, phosphorothioates, phosphoramidates, methylphosphonates, chiral-methyl phosphonates, 2-O-methyl ribonucleotides,peptide-nucleic acids (PNAs).

Unless otherwise indicated, a particular nucleic acid sequence alsoimplicitly encompasses conservatively modified variants thereof (e.g.,degenerate codon substitutions) and complementary sequences, as well asthe sequence explicitly indicated. The term nucleic acid is usedinterchangeably with gene, cDNA, mRNA, oligonucleotide, andpolynucleotide. The nucleotide sequences are displayed herein in theconventional 5′-3′ orientation.

The terms “polypeptide,” “peptide” and “protein” are usedinterchangeably herein to refer to a polymer of amino acid residues. Theterms apply to amino acid polymers in which one or more amino acidresidue is an analog or mimetic of a corresponding naturally occurringamino acid, as well as to naturally occurring amino acid polymers.Polypeptides can be modified, e.g., by the addition of carbohydrateresidues to form glycoproteins. The terms “polypeptide,” “peptide” and“protein” include glycoproteins, as well as non-glycoproteins. Thepolypeptide sequences are displayed herein in the conventionalN-terminal to C-terminal orientation.

The term “amino acid” refers to naturally occurring and synthetic aminoacids, as well as amino acid analogs and amino acid mimetics thatfunction in a manner similar to the naturally occurring amino acids.Naturally occurring amino acids are those encoded by the genetic code,as well as those amino acids that are later modified, e.g.,hydroxyproline, carboxyglutamate, and O-phosphoserine. Amino acidanalogs refers to compounds that have the same basic chemical structureas a naturally occurring amino acid, i.e., an a carbon that is bound toa hydrogen, a carboxyl group, an amino group, and an R group, e.g.,homoserine, norleucine, methionine sulfoxide, methionine, and methylsulfonium. Such analogs have modified R groups (e.g., norleucine) ormodified peptide backbones, but retain the same basic chemical structureas a naturally occurring amino acid. Amino acid mimetics refers tochemical compounds that have a structure that is different from thegeneral chemical structure of an amino acid, but that functions in amanner similar to a naturally occurring amino acid.

“Conservatively modified variants” applies to both amino acid andnucleic acid sequences. With respect to particular nucleic acidsequences, conservatively modified variants refers to those nucleicacids which encode identical or essentially identical amino acidsequences, or where the nucleic acid does not encode an amino acidsequence, to essentially identical sequences. Specifically, degeneratecodon substitutions may be achieved by generating sequences in which thethird position of one or more selected (or all) codons is substitutedwith mixed-base and/or deoxyinosine residues (Batzer et al., NucleicAcid Res. 19:5081 (1991); Ohtsuka et al., J. Biol. Chem. 260:2605-2608(1985); Rossolini et al., Mol. Cell. Probes 8:91-98 (1994)). Because ofthe degeneracy of the genetic code, a large number of functionallyidentical nucleic acids encode any given protein. For instance, thecodons GCA, GCC, GCG and GCU all encode the amino acid alanine. Thus, atevery position where an alanine is specified by a codon in an amino acidherein, the codon can be altered to any of the corresponding codonsdescribed without altering the encoded polypeptide. Such nucleic acidvariations are “silent variations,” which are one species ofconservatively modified variations. Every nucleic acid sequence hereinwhich encodes a polypeptide also describes every possible silentvariation of the nucleic acid. One of skill will recognize that eachcodon in a nucleic acid (except AUG, which is ordinarily the only codonfor methionine, and TGG, which is ordinarily the only codon fortryptophan) can be modified to yield a functionally identical molecule.Accordingly, each silent variation of a nucleic acid which encodes apolypeptide is implicit in each described sequence.

As to amino acid and nucleic acid sequences, individual substitutions,deletions or additions that alter, add or delete a single amino acid ornucleotide or a small percentage of amino acids or nucleotides in thesequence create a “conservatively modified variant,” where thealteration results in the substitution of an amino acid with achemically similar amino acid. Conservative substitution tablesproviding functionally similar amino acids are well known in the art.Such conservatively modified variants are in addition to and do notexclude polymorphic variants and alleles of the invention.

The following groups each contain amino acids that are conservativesubstitutions for one another:

1) Alanine (A), Glycine (G);

2) Serine (S), Threonine (T);

3) Aspartic acid (D), Glutamic acid (E);

4) Asparagine (N), Glutamine (Q);

5) Cysteine (C), Methionine (M);

6) Arginine (R), Lysine (K), Histidine (H);

7) Isoleucine (I), Leucine (L), Valine (V); and

8) Phenylalanine (F), Tyrosine (Y), Tryptophan (W).

(see, e.g., Creighton, Proteins (1984) for a discussion of amino acidproperties).

Design of ZFPs

The ZFPs of the invention are engineered to recognize a selected targetsite in the endogenous gene of choice. Typically, a backbone from anysuitable C₂H₂ ZFP, such as SP-1, SP-1C, or ZIF268, is used as thescaffold for the engineered ZFP (see, e.g., Jacobs, EMBO J. 11:4507(1992); Desjarlais & Berg, PNAS 90:2256-2260 (1993)). A number ofmethods can then be used to design and select a ZFP with high affinityfor its target (e.g., preferably with a K_(d) of less than about 25 nM).As described above, a ZFP can be designed or selected to bind to anysuitable target site in the target endogenous gene, with high affinity.U.S. Pat. No. 6,453,242 comprehensively describes methods for design,construction, and expression of ZFPs for selected target sites.

Any suitable method known in the art can be used to design and constructnucleic acids encoding ZFPs, e.g., phage display, random mutagenesis,combinatorial libraries, computer/rational design, affinity selection,PCR, cloning from cDNA or genomic libraries, synthetic construction andthe like. (see, e.g., U.S. Pat. No. 5,786,538; Wu et al., PNAS92:344-348 (1995); Jamieson et al., Biochemistry 33:5689-5695 (1994);Rebar & Pabo, Science 263:671-673 (1994); Choo & Klug, PNAS91:11163-11167 (1994); Choo & Klug, PNAS 91: 11168-11172 (1994);Desjarlais & Berg, PNAS 90:2256-2260 (1993); Desjarlais & Berg, PNAS89:7345-7349 (1992); Pomerantz et al., Science 267:93-96 (1995);Pomerantz et al., PNAS 92:9752-9756 (1995); and Liu et al., PNAS94:5525-5530 (1997); Griesman & Pabo, Science 275:657-661 (1997);Desjarlais & Berg, PNAS 91:11-99-11103 (1994)).

U.S. Pat. No. 6,453,242 provides methods that select a target gene, andidentify a target site within the gene containing one to six (or more)D-able sites (see definition below). Using these methods, a ZFP can thenbe synthesized that binds to the preselected site. These methods oftarget site selection are premised, in part, on the recognition that thepresence of one or more D-able sites in a target segment confers thepotential for higher binding affinity in a ZFP selected or designed tobind to that site relative to ZFPs that bind to target segments lackingD-able sites. Experimental evidence supporting this insight is providedin Examples 2-9 of U.S. Pat. No. 6,453,242.

A D-able site or subsite is a region of a target site that allows anappropriately designed single zinc finger to bind to four bases ratherthan three of the target site. Such a zinc finger binds to a triplet ofbases on one strand of a double-stranded target segment (target strand)and a fourth base on the other strand (see FIG. 2 of U.S. Pat. No.6,453,242). Binding of a single zinc finger to a four base targetsegment imposes constraints both on the sequence of the target strandand on the amino acid sequence of the zinc finger. The target sitewithin the target strand should include the “D-able” site motif 5′ NNGK3′, in which N and K are conventional IUPAC-IUB ambiguity codes. A zincfinger for binding to such a site should include an arginine residue atposition −1 and an aspartic acid, (or less preferably a glutamic acid)at position +2. The arginine residues at position −1 interacts with theG residue in the D-able site. The aspartic acid (or glutamic acid)residue at position +2 of the zinc finger interacts with the oppositestrand base complementary to the K base in the D-able site. It is theinteraction between aspartic acid (symbol D) and the opposite strandbase (fourth base) that confers the name D-able site. As is apparentfrom the D-able site formula, there are two subtypes of D-able sites: 5′NNGG 3′ and 5′ NNGT 3′. For the former site, the aspartic acid orglutamic acid at position +2 of a zinc finger interacts with a C in theopposite strand to the D-able site. In the latter site, the asparticacid or glutamic acid at position +2 of a zinc finger interacts with anA in the opposite strand to the D-able site. In general, NNGG ispreferred over NNGT.

In the design of a ZFP with three fingers, a target site should beselected in which at least one finger of the protein, and optionally,two or all three fingers have the potential to bind a D-able site. Suchcan be achieved by selecting a target site from within a larger targetgene having the formula 5′-NNx aNy bNzc-3′, wherein

each of the sets (x, a), (y, b) and (z, c) is either (N, N) or (G, K);

at least one of (x, a), (y, b) and (z, c) is (G, K). and

N and K are IUPAC-IUB ambiguity codes

In other words, at least one of the three sets (x, a), (y, b) and (z, c)is the set (G, K), meaning that the first position of the set is G andthe second position is G or T. Those of the three sets (if any) whichare not (G, K) are (N, N), meaning that the first position of the setcan be occupied by any nucleotide and the second position of the set canbe occupied by any nucleotide. As an example, the set (x, a) can be (G,K) and the sets (y, b) and (z, c) can both be (N, N).

In the formula 5′-NNx aNy bNzc-3′, the triplets of NNx aNy and bNzcrepresent the triplets of bases on the target strand bound by the threefingers in a ZFP. If only one of x, y and z is a G, and this G isfollowed by a K, the target site includes a single D-able subsite. Forexample, if only x is G, and a is K, the site reads 5′-NNG KNy bNzc-3′with the D-able subsite highlighted. If both x and y but not z are G,and a and b are K, then the target site has two overlapping D-ablesubsites as follows: 5′-NNG KNG KNz c-3′, with one such site beingrepresented in bold and the other in italics. If all three of x, y and zare G and a, b, and c are K, then the target segment includes threeD-able subsites, as follows 5′NNG KNG KNG K3′, the D-able subsites beingrepresented by bold, italics and underline.

These methods thus work by selecting a target gene, and systematicallysearching within the possible subsequences of the gene for target sitesconforming to the formula 5′-NNx aNy bNzc-3′, as described above. Insome such methods, every possible subsequence of 10 contiguous bases oneither strand of a potential target gene is evaluated to determinewhether it conforms to the above formula, and, if so, how many D-ablesites are present. Typically, such a comparison is performed bycomputer, and a list of target sites conforming to the formula areoutput. Optionally, such target sites can be output in different subsetsaccording to how many D-able sites are present.

In a variation, the methods of the invention identify first and secondtarget segments, each independently conforming to the above formula. Thetwo target segments in such methods are constrained to be adjacent orproximate (i.e., within about 0-5 bases) of each other in the targetgene. The strategy underlying selection of proximate target segments isto allow the design of a ZFP formed by linkage of two component ZFPsspecific for the first and second target segments respectively. Theseprinciples can be extended to select target sites to be bound by ZFPswith any number of component fingers. For example, a suitable targetsite for a nine finger protein would have three component segments, eachconforming to the above formula.

The target sites identified by the above methods can be subject tofurther evaluation by other criteria or can be used directly for designor selection (if needed) and production of a ZFP specific for such asite. A further criteria for evaluating potential target sites is theirproximity to particular regions within a gene. If a ZFP is to be used torepress a cellular gene on its own (i.e., without linking the ZFP to arepressing moiety), then the optimal location appears to be at, orwithin 50 bp upstream or downstream of the site of transcriptioninitiation, to interfere with the formation of the transcription complex(Kim & Pabo, J. Biol. Chem. 272:29795-296800 (1997)) or compete for anessential enhancer binding protein. If, however, a ZFP is fused to afunctional domain such as the KRAB repressor domain or the VP16activator domain, the location of the binding site is considerably moreflexible and can be outside known regulatory regions. For example, aKRAB domain can repress transcription at a promoter up to at least 3 kbpfrom where KRAB is bound (Margolin et al., PNAS 91:4509-4513 (1994)).Thus, target sites can be selected that do not necessarily include oroverlap segments of demonstrable biological significance with targetgenes, such as regulatory sequences. Other criteria for furtherevaluating target segments include the prior availability of ZFPsbinding to such segments or related segments, and/or ease of designingnew ZFPs to bind a given target segment.

After a target segment has been selected, a ZFP that binds to thesegment can be provided by a variety of approaches. The simplest ofapproaches is to provide a precharacterized ZFP from an existingcollection that is already known to bind to the target site. However, inmany instances, such ZFPs do not exist. An alternative approach can alsobe used to design new ZFPs, which uses the information in a database ofexisting ZFPs and their respective binding affinities. A furtherapproach is to design a ZFP based on substitution rules as discussedabove. A still further alternative is to select a ZFP with specificityfor a given target by an empirical process such as phage display. Insome such methods, each component finger of a ZFP is designed orselected independently of other component fingers. For example, eachfinger can be obtained from a different preexisting ZFP or each fingercan be subject to separate randomization and selection.

Once a ZFP has been selected, designed, or otherwise provided to a giventarget segment, the ZFP or the DNA encoding it are synthesized.Exemplary methods for synthesizing and expressing DNA encoding zincfinger proteins are described below. The ZFP or a polynucleotideencoding it can then be used for modulation of expression, or analysisof the target gene containing the target site to which the ZFP binds.

Expression and Purification of ZFPs

ZFP polypeptides and nucleic acids can be made using routine techniquesin the field of recombinant genetics. Basic texts disclosing the generalmethods of use in this invention include Sambrook et al., MolecularCloning, A Laboratory Manual (2nd ed. 1989); Kriegler, Gene Transfer andExpression: A Laboratory Manual (1990); and Current Protocols inMolecular Biology (Ausubel et al., eds., 1994)). In addition,essentially any nucleic acid can be custom ordered from any of a varietyof commercial sources. Similarly, peptides and antibodies can be customordered from any of a variety of commercial sources.

Two alternative methods are typically used to create the codingsequences required to express newly designed DNA-binding peptides. Oneprotocol is a PCR-based assembly procedure that utilizes six overlappingoligonucleotides (FIG. 1). Three oligonucleotides (oligos 1, 3, and 5 inFIG. 1) correspond to “universal” sequences that encode portions of theDNA-binding domain between the recognition helices. Theseoligonucleotides remain constant for all zinc finger constructs. Theother three “specific” oligonucleotides (oligos 2, 4, and 6 in FIG. 1)are designed to encode the recognition helices. These oligonucleotidescontain substitutions primarily at positions −1, 2, 3 and 6 on therecognition helices making them specific for each of the differentDNA-binding domains.

The PCR synthesis is carried out in two steps. First, a double strandedDNA template is created by combining the six oligonucleotides (threeuniversal, three specific) in a four cycle PCR reaction with a lowtemperature annealing step, thereby annealing the oligonucleotides toform a DNA “scaffold.” The gaps in the scaffold are filled in byhigh-fidelity thermostable polymerase, the combination of Taq and Pfupolymerases also suffices. In the second phase of construction, the zincfinger template is amplified by external primers designed to incorporaterestriction sites at either end for cloning into a shuttle vector ordirectly into an expression vector.

An alternative method of cloning the newly designed DNA-binding proteinsrelies on annealing complementary oligonucleotides encoding the specificregions of the desired ZFP. This particular application requires thatthe oligonucleotides be phosphorylated prior to the final ligation step.This is usually performed before setting up the annealing reactions, butkinasing can also occur post-annealing. In brief, the “universal”oligonucleotides encoding the constant regions of the proteins (oligos1, 2 and 3 of above) are annealed with their complementaryoligonucleotides. Additionally, the “specific” oligonucleotides encodingthe finger recognition helices are annealed with their respectivecomplementary oligonucleotides. These complementary oligos are designedto fill in the region which was previously filled in by polymerase inthe protocol described above. The complementary oligos to the commonoligos 1 and finger 3 are engineered to leave overhanging sequencesspecific for the restriction sites used in cloning into the vector ofchoice. The second assembly protocol differs from the initial protocolin the following aspects: the “scaffold” encoding the newly designed ZFPis composed entirely of synthetic DNA thereby eliminating the polymerasefill-in step, additionally the fragment to be cloned into the vectordoes not require amplification. Lastly, the design of leavingsequence-specific overhangs eliminates the need for restriction enzymedigests of the inserting fragment.

The resulting fragment encoding the newly designed ZFP is ligated intoan expression vector. Expression vectors that are commonly utilizedinclude, but are not limited to, a modified pMAL-c2 bacterial expressionvector (New England BioLabs, “NEB”) or a eukaryotic expression vector,pcDNA (Promega).

Any suitable method of protein purification known to those of skill inthe art can be used to purify ZFPs of the invention (see Ausubel, supra,Sambrook, supra). In addition, any suitable host can be used, e.g.,bacterial cells, insect cells, yeast cells, mammalian cells, and thelike.

In one embodiment, expression of the ZFP fused to a maltose bindingprotein (MBP-ZFP) in bacterial strain JM109 allows for straightforwardpurification through an amylose column (NEB). High expression levels ofthe zinc finger chimeric protein can be obtained by induction with IPTGsince the MBP-ZFP fusion in the pMal-c2 expression plasmid is under thecontrol of the IPTG inducible tac promoter (NEB). Bacteria containingthe MBP-ZFP fusion plasmids are inoculated in to 2xYT medium containing10 μM ZnCl₂, 0.02% glucose, plus 50 μg/ml ampicillin and shaken at 37°C. At mid-exponential growth IPTG is added to 0.3 mM and the culturesare allowed to shake. After 3 hours the bacteria are harvested bycentrifugation, disrupted by sonication, and then insoluble material isremoved by centrifugation. The MBP-ZFP proteins are captured on anamylose-bound resin, washed extensively with buffer containing 20 mMTris-HCl (pH 7.5), 200 mM NaCl, 5 mM DTT and 50 μM ZnCl₂, then elutedwith maltose in essentially the same buffer (purification is based on astandard protocol from NEB). Purified proteins are quantitated andstored for biochemical analysis.

The biochemical properties of the purified proteins, e.g., K_(d), can becharacterized by any suitable assay. In one embodiment, K_(d) ischaracterized via electrophoretic mobility shift assays (“EMSA”)(Buratowski & Chodosh, in Current Protocols in Molecular Biology pp.12.2.1-12.2.7 (Ausubel ed., 1996); see also U.S. Pat. No. 5,789,538.Affinity is measured by titrating purified protein against a low fixedamount of labeled double-stranded oligonucleotide target. The targetcomprises the natural binding site sequence (9 or 18 bp) flanked by the3 bp found in the natural sequence. External to the binding site plusflanking sequence is a constant sequence. The annealed oligonucleotidetargets possess a 1 bp 5′ overhang which allows for efficient labelingof the target with T4 phage polynucleotide kinase. For the assay thetarget is added at a concentration of 40 nM or lower (the actualconcentration is kept at least 10-fold lower than the lowest proteindilution) and the reaction is allowed to equilibrate for at least 45min. In addition the reaction mixture also contains 10 mM Tris (pH 7.5),100 mM KCl, 1 mM MgCl₂, 0.1 mM ZnCl₂, 5 mM DTT, 10% glycerol, 0.02% BSA(poly (dIdC) or (dAdT) (Pharmacia) can also added at 10-100 μg/μl).

The equilibrated reactions are loaded onto a 10% polyacrylamide gel,which has been pre-run for 45 min in Tris/glycine buffer, then bound andunbound labeled target is resolved be electrophoresis at 150V(alternatively, 10-20% gradient Tris-HCl gels, containing a 4%polyacrylamide stacker, can be used). The dried gels are visualized byautoradiography or phosphoroimaging and the apparent K_(d) is determinedby calculating the protein concentration that gives half-maximalbinding.

Similar assays can also include determining active fractions in theprotein preparations. Active fractions are determined by stoichiometricgel shifts where proteins are titrated against a high concentration oftarget DNA. Titrations are done at 100, 50, and 25% of target (usuallyat micromolar levels).

In another embodiment, phage display libraries can be used to selectZFPs with high affinity to the selected target site. This method differsfundamentally from direct design in that it involves the generation ofdiverse libraries of mutagenized ZFPs, followed by the isolation ofproteins with desired DNA-binding properties using affinity selectionmethods. To use this method, the experimenter typically proceeds asfollows.

First, a gene for a ZFP is mutagenized to introduce diversity intoregions important for binding specificity and/or affinity. In a typicalapplication, this is accomplished via randomization of a single fingerat positions −1, +2, +3, and +6, and perhaps accessory positions such as+1, +5, +8, or +10.

Next, the mutagenized gene is cloned into a phage or phagemid vector asa fusion with, e.g., gene III of filamentous phage, which encodes thecoat protein pIII. The zinc finger gene is inserted between segments ofgene III encoding the membrane export signal peptide and the remainderof pIII, so that the ZFP is expressed as an amino-terminal fusion withpIII in the mature, processed protein. When using phagemid vectors, themutagenized zinc finger gene may also be fused to a truncated version ofgene III encoding, minimally, the C-terminal region required forassembly of pIII into the phage particle.

The resultant vector library is transformed into E. coli and used toproduce filamentous phage which express variant ZFPs on their surface asfusions with the coat protein pIII (if a phagemid vector is used, thenthe this step requires superinfection with helper phage). The phagelibrary is then incubated with target DNA site, and affinity selectionmethods are used to isolate phage which bind target with high affinityfrom bulk phage. Typically, the DNA target is immobilized on a solidsupport, which is then washed under conditions sufficient to remove allbut the tightest binding phage. After washing, any phage remaining onthe support are recovered via elution under conditions which totallydisrupt zinc finger-DNA binding.

Recovered phage are used to infect fresh E. coli, which is thenamplified and used to produce a new batch of phage particles. Thebinding and recovery steps are then repeated as many times as isnecessary to sufficiently enrich the phage pool for tight binders suchthat these may be identified using sequencing and/or screening methods.

Regulatory Domains

The ZFPs of the invention can optionally be associated with regulatorydomains for modulation of gene expression. The ZFP can be covalently ornon-covalently associated with one or more regulatory domains,alternatively two or more regulatory domains, with the two or moredomains being two copies of the same domain, or two different domains.The regulatory domains can be covalently linked to the ZFP, e.g., via anamino acid linker, as part of a fusion protein. The ZFPs can also beassociated with a regulatory domain via a non-covalent dimerizationdomain, e.g., a leucine zipper, a STAT protein N terminal domain, or anFK506 binding protein (see, e.g., O'Shea, Science 254: 539 (1991),Barahmand-Pour et al., Curr. Top. Microbiol. Immunol. 211:121-128(1996); Klemm et al., Annu. Rev. Immunol. 16:569-592 (1998); Klemm etal., Annu. Rev. Immunol. 16:569-592 (1998); Ho et al., Nature382:822-826 (1996); and Pomeranz et al., Biochem. 37:965 (1998)). Theregulatory domain can be associated with the ZFP at any suitableposition, including the C- or N-terminus of the ZFP.

Common regulatory domains for addition to the ZFP include, e.g.,effector domains from transcription factors (activators, repressors,co-activators, co-repressors), silencers, nuclear hormone receptors,oncogene transcription factors (e.g., myc, jun, fos, myb, max, mad, rel,ets, bcl, myb, mos family members etc.); DNA repair enzymes and theirassociated factors and modifiers; DNA rearrangement enzymes and theirassociated factors and modifiers; chromatin associated proteins andtheir modifiers (e.g., kinases, acetylases and deacetylases); and DNAmodifying enzymes (e.g., methyltransferases, topoisomerases, helicases,ligases, kinases, phosphatases, polymerases, endonucleases) and theirassociated factors and modifiers.

Transcription factor polypeptides from which one can obtain a regulatorydomain include those that are involved in regulated and basaltranscription. Such polypeptides include transcription factors, theireffector domains, coactivators, silencers, nuclear hormone receptors(see, e.g., Goodrich et al., Cell 84:825-30 (1996) for a review ofproteins and nucleic acid elements involved in transcription;transcription factors in general are reviewed in Barnes & Adcock, Clin.Exp. Allergy 25 Suppl. 2:46-9 (1995) and Roeder, Methods Enzymol.273:165-71 (1996)). Databases dedicated to transcription factors areknown (see, e.g., Science 269:630 (1995)). Nuclear hormone receptortranscription factors are described in, for example, Rosen et al., J.Med. Chem. 38:4855-74 (1995). The C/EBP family of transcription factorsare reviewed in Wedel et al., Immunobiology 193:171-85 (1995).Coactivators and co-repressors that mediate transcription regulation bynuclear hormone receptors are reviewed in, for example, Meier, Eur. J.Endocrinol. 134(2):158-9 (1996); Kaiser et al., Trends Biochem. Sci.21:342-5 (1996); and Utley et al., Nature 394:498-502 (1998)). GATAtranscription factors, which are involved in regulation ofhematopoiesis, are described in, for example, Simon, Nat. Genet. 11:9-11(1995); Weiss et al., Exp. Hematol. 23:99-107. TATA box binding protein(TBP) and its associated TAF polypeptides (which include TAF30, TAF55,TAF80, TAF110, TAF150, and TAF250) are described in Goodrich & Tjian,Curr. Opin. Cell Biol. 6:403-9 (1994) and Hurley, Curr. Opin. Struct.Biol. 6:69-75 (1996). The STAT family of transcription factors arereviewed in, for example, Barahmand-Pour et al., Curr. Top. Microbiol.Immunol. 211:121-8 (1996). Transcription factors involved in disease arereviewed in Aso et al., J. Clin. Invest. 97:1561-9 (1996).

In one embodiment, the KRAB repression domain from the human KOX-1protein is used as a transcriptional repressor (Thiesen et al., NewBiologist 2:363-374 (1990); Margolin et al., PNAS 91:4509-4513 (1994);Pengue et al., Nucl. Acids Res. 22:2908-2914 (1994); Witzgall et al.,PNAS 91:4514-4518 (1994); see also Example III)). In another embodiment,KAP-1, a KRAB co-repressor, is used with KRAB (Friedman et al., GenesDev. 10:2067-2078 (1996)). Alternatively, KAP-1 can be used alone with aZFP. Other preferred transcription factors and transcription factordomains that act as transcriptional repressors include MAD (see, e.g.,Sommer et al., J. Biol. Chem. 273:6632-6642 (1998); Gupta et al.,Oncogene 16:1149-1159 (1998); Queva et al., Oncogene 16:967-977 (1998);Larsson et al., Oncogene 15:737-748 (1997); Laherty et al., Cell89:349-356 (1997); and Cultraro et al., Mol Cell. Biol. 17:2353-2359(19977)); FKHR (forkhead in rhapdosarcoma gene; Ginsberg et al., CancerRes. 15:3542-3546 (1998); Epstein et al., Mol. Cell. Biol. 18:4118-4130(1998)); EGR-1 (early growth response gene product-1; Yan et al., PNAS95:8298-8303 (1998); and Liu et al., Cancer Gene Ther. 5:3-28 (1998));the ets2 repressor factor repressor domain (ERD; Sgouras et al., EMBO J.14:4781-4793 ((19095)); and the MAD smSIN3 interaction domain (SID; Ayeret al., Mol. Cell. Biol. 16:5772-5781 (1996)).

In one embodiment, the HSV VP16 activation domain is used as atranscriptional activator (see, e.g., Hagmann et al., J. Virol.71:5952-5962 (1997)). Other preferred transcription factors that couldsupply activation domains include the VP64 activation domain (Seipel etal., EMBO J. 11:4961-4968 (1996)); nuclear hormone receptors (see, e.g.,Torchia et al., Curr. Opin. Cell. Biol. 10:373-383 (1998)); the p65subunit of nuclear factor kappa B (Bitko & Barik, J. Virol. 72:5610-5618(1998) and Doyle & Hunt, Neuroreport 8:2937-2942 (1997)); and EGR-1(early growth response gene product-1; Yan et al., PNAS 95:8298-8303(1998); and Liu et al., Cancer Gene Ther. 5:3-28 (1998)).

Kinases, phosphatases, and other proteins that modify polypeptidesinvolved in gene regulation are also useful as regulatory domains forZFPs. Such modifiers are often involved in switching on or offtranscription mediated by, for example, hormones. Kinases involved intranscription regulation are reviewed in Davis, Mol. Reprod. Dev.42:459-67 (1995), Jackson et al., Adv. Second Messenger PhosphoproteinRes. 28:279-86 (1993), and Boulikas, Crit. Rev. Eukaryot. Gene Expr.5:1-77 (1995), while phosphatases are reviewed in, for example,Schonthal & Semin, Cancer Biol. 6:239-48 (1995). Nuclear tyrosinekinases are described in Wang, Trends Biochem. Sci. 19:373-6 (1994).

As described, useful domains can also be obtained from the gene productsof oncogenes (e.g., myc, jun, fos, myb, max, mad, rel, ets, bcl, myb,mos family members) and their associated factors and modifiers.Oncogenes are described in, for example, Cooper, Oncogenes, 2nd ed., TheJones and Bartlett Series in Biology, Boston, Mass., Jones and BartlettPublishers, 1995. The ets transcription factors are reviewed in Waslylket al., Eur. J. Biochem. 211:7-18 (1993) and Crepieux et al., Crit. Rev.Oncog. 5:615-38 (1994). Myc oncogenes are reviewed in, for example, Ryanet al., Biochem. J. 314:713-21 (1996). The jun and fos transcriptionfactors are described in, for example, The Fos and Jun Families ofTranscription Factors, Angel & Herrlich, eds. (1994). The max oncogeneis reviewed in Hurlin et al., Cold Spring Harb. Symp. Quant. Biol.59:109-16. The myb gene family is reviewed in Kanei-Ishii et al., Curr.Top. Microbiol. Immunol. 211:89-98 (1996). The mos family is reviewed inYew et al., Curr. Opin. Genet. Dev. 3:19-25 (1993).

ZFPs can include regulatory domains obtained from DNA repair enzymes andtheir associated factors and modifiers. DNA repair systems are reviewedin, for example, Vos, Curr. Opin. Cell Biol. 4:385-95 (1992); Sancar,Ann. Rev. Genet. 29:69-105 (1995); Lehmann, Genet. Eng. 17:1-19 (1995);and Wood, Ann. Rev. Biochem. 65:135-67 (1996). DNA rearrangement enzymesand their associated factors and modifiers can also be used asregulatory domains (see, e.g., Gangloff et al., Experientia 50:261-9(1994); Sadowski, FASEB J. 7:760-7 (1993)).

Similarly, regulatory domains can be derived from DNA modifying enzymes(e.g., DNA methyltransferases, topoisomerases, helicases, ligases,kinases, phosphatases, polymerases) and their associated factors andmodifiers. Helicases are reviewed in Matson et al., Bioessays, 16:13-22(1994), and methyltransferases are described in Cheng, Curr. Opin.Struct. Biol. 5:4-10 (1995). Chromatin associated proteins and theirmodifiers (e.g., kinases, acetylases and deacetylases), such as histonedeacetylase (Wolffe, Science 272:371-2 (1996)) are also useful asdomains for addition to the ZFP of choice. In one preferred embodiment,the regulatory domain is a DNA methyl transferase that acts as atranscriptional repressor (see, e.g., Van den Wyngaert et al., FEBSLett. 426:283-289 (1998); Flynn et al., J. Mol. Biol. 279:101-116(1998); Okano et al., Nucleic Acids Res. 26:2536-2540 (1998); and Zardo& Caiafa, J. Biol. Chem. 273:16517-16520 (1998)). In another preferredembodiment, endonucleases such as Fok1 are used as transcriptionalrepressors, which act via gene cleavage (see, e.g., WO95/09233; andPCT/US94/01201).

Factors that control chromatin and DNA structure, movement andlocalization and their associated factors and modifiers; factors derivedfrom microbes (e.g., prokaryotes, eukaryotes and virus) and factors thatassociate with or modify them can also be used to obtain chimericproteins. In one embodiment, recombinases and integrases are used asregulatory domains. In one embodiment, histone acetyltransferase is usedas a transcriptional activator (see, e.g., Jin & Scotto, Mol. Cell.Biol. 18:4377-4384 (1998); Wolffe, Science 272:371-372 (1996); Tauntonet al., Science 272:408-411 (1996); and Hassig et al., PNAS 95:3519-3524(1998)). In another embodiment, histone deacetylase is used as atranscriptional repressor (see, e.g., Jin & Scotto, Mol. Cell. Biol.18:4377-4384 (1998); Syntichaki & Thireos, J. Biol. Chem.273:24414-24419 (1998); Sakaguchi et al., Genes Dev. 12:2831-2841(1998); and Martinez et al., J. Biol. Chem. 273:23781-23785 (1998)).

Linker domains between polypeptide domains, e.g., between two ZFPs orbetween a ZFP and a regulatory domain, can be included. Such linkers aretypically polypeptide sequences, such as poly gly sequences of betweenabout 5 and 200 amino acids. Preferred linkers are typically flexibleamino acid subsequences which are synthesized as part of a recombinantfusion protein. For example, in one embodiment, the linker DGGGS is usedto link two ZFPs. In another embodiment, the flexible linker linking twoZFPs is an amino acid subsequence comprising the sequence TGEKP (see,e.g., Liu et al., PNAS 5525-5530 (1997)). In another embodiment, thelinker LRQKDGERP is used to link two ZFPs. In another embodiment, thefollowing linkers are used to link two ZFPs: GGRR (Pomerantz et al.1995, supra), (G4S)_(n) (Kim et al., PNAS 93, 1156-1160 (1996.); andGGRRGGGS; LRQRDGERP; LRQKDGGGSERP; LRQKd(G3S)₂ ERP. Alternatively,flexible linkers can be rationally designed using computer programcapable of modeling both DNA-binding sites and the peptides themselves(Desjarlais & Berg, PNAS 90:2256-2260 (1993), PNAS 91:11099-11103 (1994)or by phage display methods.

In other embodiments, a chemical linker is used to connect syntheticallyor recombinantly produced domain sequences. Such flexible linkers areknown to persons of skill in the art. For example, poly(ethylene glycol)linkers are available from Shearwater Polymers, Inc. Huntsville, Ala.These linkers optionally have amide linkages, sulfhydryl linkages, orheterofunctional linkages. In addition to covalent linkage of ZFPs toregulatory domains, non-covalent methods can be used to producemolecules with ZFPs associated with regulatory domains.

In addition to regulatory domains, often the ZFP is expressed as afusion protein such as maltose binding protein (“MBP”), glutathione Stransferase (GST), hexahistidine, c-myc, and the FLAG epitope, for easeof purification, monitoring expression, or monitoring cellular andsubcellular localization.

Expression Vectors for Nucleic Acids Encoding ZFP

The nucleic acid encoding the ZFP of choice is typically cloned intointermediate vectors for transformation into prokaryotic or eukaryoticcells for replication and/or expression, e.g., for determination ofK_(d). Intermediate vectors are typically prokaryote vectors, e.g.,plasmids, or shuttle vectors, or insect vectors, for storage ormanipulation of the nucleic acid encoding ZFP or production of protein.The nucleic acid encoding a ZFP is also typically cloned into anexpression vector, for administration to a plant cell, animal cell,preferably a mammalian cell or a human cell, fungal cell, bacterialcell, or protozoal cell.

To obtain expression of a cloned gene or nucleic acid, a ZFP istypically subcloned into an expression vector that contains a promoterto direct transcription. Suitable bacterial and eukaryotic promoters arewell known in the art and described, e.g., in Sambrook et al., MolecularCloning, A Laboratory Manual (2nd ed. 1989); Kriegler, Gene Transfer andExpression: A Laboratory Manual (1990); and Current Protocols inMolecular Biology (Ausubel et al., eds., 1994). Bacterial expressionsystems for expressing the ZFP are available in, e.g., E. coli, Bacillussp., and Salmonella (Palva et al., Gene 22:229-235 (1983)). Kits forsuch expression systems are commercially available. Eukaryoticexpression systems for mammalian cells, yeast, and insect cells are wellknown in the art and are also commercially available.

The promoter used to direct expression of a ZFP nucleic acid depends onthe particular application. For example, a strong constitutive promoteris typically used for expression and purification of ZFP. In contrast,when a ZFP is administered in vivo for gene regulation, either aconstitutive or an inducible promoter is used, depending on theparticular use of the ZFP. In addition, a preferred promoter foradministration of a ZFP can be a weak promoter, such as HSV TK or apromoter having similar activity. The promoter typically can alsoinclude elements that are responsive to transactivation, e.g., hypoxiaresponse elements, Gal4 response elements, lac repressor responseelement, and small molecule control systems such as tet-regulatedsystems and the RU-486 system (see, e.g., Gossen & Bujard, PNAS 89:5547(1992); Oligino et al., Gene Ther. 5:491-496 (1998); Wang et al., GeneTher. 4:432-441 (1997); Neering et al., Blood 88:1147-1155 (1996); andRendahl et al., Nat. Biotechnol. 16:757-761 (1998)).

In addition to the promoter, the expression vector typically contains atranscription unit or expression cassette that contains all theadditional elements required for the expression of the nucleic acid inhost cells, either prokaryotic or eukaryotic. A typical expressioncassette thus contains a promoter operably linked, e.g., to the nucleicacid sequence encoding the ZFP, and signals required, e.g., forefficient polyadenylation of the transcript, transcriptionaltermination, ribosome binding sites, or translation termination.Additional elements of the cassette may include, e.g., enhancers, andheterologous spliced intronic signals.

The particular expression vector used to transport the geneticinformation into the cell is selected with regard to the intended use ofthe ZFP, e.g., expression in plants, animals, bacteria, fungus, protozoaetc. (see expression vectors described below and in the Examplesection). Standard bacterial expression vectors include plasmids such aspBR322 based plasmids, pSKF, pET23D, and commercially available fusionexpression systems such as GST and LacZ. A preferred fusion protein isthe maltose binding protein, “MBP.” Such fusion proteins are used forpurification of the ZFP. Epitope tags can also be added to recombinantproteins to provide convenient methods of isolation, for monitoringexpression, and for monitoring cellular and subcellular localization,e.g., c-myc or FLAG.

Expression vectors containing regulatory elements from eukaryoticviruses are often used in eukaryotic expression vectors, e.g., SV40vectors, papilloma virus vectors, and vectors derived from Epstein-Barrvirus. Other exemplary eukaryotic vectors include pMSG, pAV009/A+,pMTO10/A+, pMAMneo-5, baculovirus pDSVE, and any other vector allowingexpression of proteins under the direction of the SV40 early promoter,SV40 late promoter, metallothionein promoter, murine mammary tumor viruspromoter, Rous sarcoma virus promoter, polyhedrin promoter, or otherpromoters shown effective for expression in eukaryotic cells.

Some expression systems have markers for selection of stably transfectedcell lines such as thymidine kinase, hygromycin B phosphotransferase,and dihydrofolate reductase. High yield expression systems are alsosuitable, such as using a baculovirus vector in insect cells, with a ZFPencoding sequence under the direction of the polyhedrin promoter orother strong baculovirus promoters.

The elements that are typically included in expression vectors alsoinclude a replicon that functions in E. coli, a gene encoding antibioticresistance to permit selection of bacteria that harbor recombinantplasmids, and unique restriction sites in nonessential regions of theplasmid to allow insertion of recombinant sequences.

Standard transfection methods are used to produce bacterial, mammalian,yeast or insect cell lines that express large quantities of protein,which are then purified using standard techniques (see, e.g., Colley etal., J. Biol. Chem. 264:17619-17622 (1989); Guide to ProteinPurification, in Methods in Enzymology, vol. 182 (Deutscher, ed.,1990)). Transformation of eukaryotic and prokaryotic cells are performedaccording to standard techniques (see, e.g., Morrison, J. Bact.132:349-351 (1977); Clark-Curtiss & Curtiss, Methods in Enzymology101:347-362 (Wu et al., eds, 1983).

Any of the well known procedures for introducing foreign nucleotidesequences into host cells may be used. These include the use of calciumphosphate transfection, polybrene, protoplast fusion, electroporation,liposomes, microinjection, naked DNA, plasmid vectors, viral vectors,both episomal and integrative, and any of the other well known methodsfor introducing cloned genomic DNA, cDNA, synthetic DNA or other foreigngenetic material into a host cell (see, e.g., Sambrook et al., supra).It is only necessary that the particular genetic engineering procedureused be capable of successfully introducing at least one gene into thehost cell capable of expressing the protein of choice.

Assays for Determining Regulation of Gene Expression by ZFPs

A variety of assays can be used to determine the level of geneexpression regulation by ZFPs. The activity of a particular ZFP can beassessed using a variety of in vitro and in vivo assays, by measuring,e.g., protein or mRNA levels, product levels, enzyme activity, tumorgrowth; transcriptional activation or repression of a reporter gene;second messenger levels (e.g., cGMP, cAMP, IP3, DAG, Ca²⁺); cytokine andhormone production levels; and neovascularization, using, e.g.,immunoassays (e.g., ELISA and immunohistochemical assays withantibodies), hybridization assays (e.g., RNase protection, northerns, insitu hybridization, oligonucleotide array studies), colorimetric assays,amplification assays, enzyme activity assays, tumor growth assays,phenotypic assays, and the like.

ZFPs are typically first tested for activity in vitro using culturedcells, e.g., 293 cells, CHO cells, VERO cells, BHK cells, HeLa cells,COS cells, and the like. Preferably, human cells are used. The ZFP isoften first tested using a transient expression system with a reportergene, and then regulation of the target endogenous gene is tested incells and in animals, both in vivo and ex vivo. The ZFP can berecombinantly expressed in a cell, recombinantly expressed in cellstransplanted into an animal, or recombinantly expressed in a transgenicanimal, as well as administered as a protein to an animal or cell usingdelivery vehicles described below. The cells can be immobilized, be insolution, be injected into an animal, or be naturally occurring in atransgenic or non-transgenic animal.

Modulation of gene expression is tested using one of the in vitro or invivo assays described herein. Samples or assays are treated with a ZFPand compared to control samples without the test compound, to examinethe extent of modulation. As described above, for regulation ofendogenous gene expression, the ZFP typically has a K_(d) of 200 nM orless, more preferably 100 nM or less, more preferably 50 nM, mostpreferably 25 nM or less.

The effects of the ZFPs can be measured by examining any of theparameters described above. Any suitable gene expression, phenotypic, orphysiological change can be used to assess the influence of a ZFP. Whenthe functional consequences are determined using intact cells oranimals, one can also measure a variety of effects such as tumor growth,neovascularization, hormone release, transcriptional changes to bothknown and uncharacterized genetic markers (e.g., northern blots oroligonucleotide array studies), changes in cell metabolism such as cellgrowth or pH changes, and changes in intracellular second messengerssuch as cGMP.

Preferred assays for ZFP regulation of endogenous gene expression can beperformed in vitro. In one preferred in vitro assay format, ZFPregulation of endogenous gene expression in cultured cells is measuredby examining protein production using an ELISA assay (see Examples VIand VII). The test sample is compared to control cells treated with anempty vector or an unrelated ZFP that is targeted to another gene.

In another embodiment, ZFP regulation of endogenous gene expression isdetermined in vitro by measuring the level of target gene mRNAexpression. The level of gene expression is measured usingamplification, e.g., using PCR, LCR, or hybridization assays, e.g.,northern hybridization, RNase protection, dot blotting. RNase protectionis used in one embodiment (see Example VIII and FIG. 10). The level ofprotein or mRNA is detected using directly or indirectly labeleddetection agents, e.g., fluorescently or radioactively labeled nucleicacids, radioactively or enzymatically labeled antibodies, and the like,as described herein.

Alternatively, a reporter gene system can be devised using the targetgene promoter operably linked to a reporter gene such as luciferase,green fluorescent protein, CAT, or β-gal. The reporter construct istypically co-transfected into a cultured cell. After treatment with theZFP of choice, the amount of reporter gene transcription, translation,or activity is measured according to standard techniques known to thoseof skill in the art.

Another example of a preferred assay format useful for monitoring ZFPregulation of endogenous gene expression is performed in vivo. Thisassay is particularly useful for examining ZFPs that inhibit expressionof tumor promoting genes, genes involved in tumor support, such asneovascularization (e.g., VEGF), or that activate tumor suppressor genessuch as p53. In this assay, cultured tumor cells expressing the ZFP ofchoice are injected subcutaneously into an immune compromised mouse suchas an athymic mouse, an irradiated mouse, or a SCID mouse. After asuitable length of time, preferably 4-8 weeks, tumor growth is measured,e.g., by volume or by its two largest dimensions, and compared to thecontrol. Tumors that have statistically significant reduction (using,e.g., Student's T test) are said to have inhibited growth.Alternatively, the extent of tumor neovascularization can also bemeasured. Immunoassays using endothelial cell specific antibodies areused to stain for vascularization of the tumor and the number of vesselsin the tumor. Tumors that have a statistically significant reduction inthe number of vessels (using, e.g., Student's T test) are said to haveinhibited neovascularization.

Transgenic and non-transgenic animals are also used as a preferredembodiment for examining regulation of endogenous gene expression invivo. Transgenic animals typically express the ZFP of choice.Alternatively, animals that transiently express the ZFP of choice, or towhich the ZFP has been administered in a delivery vehicle, can be used.Regulation of endogenous gene expression is tested using any one of theassays described herein.

Nucleic Acids Encoding ZFPs and Gene Therapy

Conventional viral and non-viral based gene transfer methods can be usedto introduce nucleic acids encoding engineered ZFP in mammalian cells ortarget tissues. Such methods can be used to administer nucleic acidsencoding ZFPs to cells in vitro. Preferably, the nucleic acids encodingZFPs are administered for in vivo or ex vivo gene therapy uses.Non-viral vector delivery systems include DNA plasmids, naked nucleicacid, and nucleic acid complexed with a delivery vehicle such as aliposome. Viral vector delivery systems include DNA and RNA viruses,which have either episomal or integrated genomes after delivery to thecell. For a review of gene therapy procedures, see Anderson, Science256:808-813 (1992); Nabel & Felgner, TIBTECH 11:211-217 (1993); Mitani &Caskey, TIBTECH 11:162-166 (1993); Dillon, TIBTECH 11:167-175 (1993);Miller, Nature 357:455-460 (1992); Van Brunt, Biotechnology6(10):1149-1154 (1988); Vigne, Restorative Neurology and Neuroscience8:35-36 (1995); Kremer & Perricaudet, British Medical Bulletin51(1):31-44 (1995); Haddada et al., in Current Topics in Microbiologyand Immunology Doerfler and Bohm (eds) (1995); and Yu et al., GeneTherapy 1:13-26 (1994).

Methods of non-viral delivery of nucleic acids encoding engineered ZFPsinclude lipofection, microinjection, biolistics, virosomes, liposomes,immunoliposomes, polycation or lipid:nucleic acid conjugates, naked DNA,artificial virions, and agent-enhanced uptake of DNA. Lipofection isdescribed in e.g., U.S. Pat. No. 5,049,386, U.S. Pat. No. 4,946,787; andU.S. Pat. No. 4,897,355) and lipofection reagents are sold commercially(e.g., Transfectam™ and Lipofectin™). Cationic and neutral lipids thatare suitable for efficient receptor-recognition lipofection ofpolynucleotides include those of Felgner, WO 91/17424, WO 91/16024.Delivery can be to cells (ex vivo administration) or target tissues (invivo administration).

The preparation of lipid:nucleic acid complexes, including targetedliposomes such as immunolipid complexes, is well known to one of skillin the art (see, e.g., Crystal, Science 270:404-410 (1995); Blaese etal., Cancer Gene Ther. 2:291-297 (1995); Behr et al., Bioconjugate Chem.5:382-389 (1994); Remy et al., Bioconjugate Chem. 5:647-654 (1994); Gaoet al., Gene Therapy 2:710-722 (1995); Ahmad et al., Cancer Res.52:4817-4820 (1992); U.S. Pat. Nos. 4,186,183, 4,217,344, 4,235,871,4,261,975, 4,485,054, 4,501,728, 4,774,085, 4,837,028, and 4,946,787).

The use of RNA or DNA viral based systems for the delivery of nucleicacids encoding engineered ZFP take advantage of highly evolved processesfor targeting a virus to specific cells in the body and trafficking theviral payload to the nucleus. Viral vectors can be administered directlyto patients (in vivo) or they can be used to treat cells in vitro andthe modified cells are administered to patients (ex vivo). Conventionalviral based systems for the delivery of ZFPs could include retroviral,lentivirus, adenoviral, adeno-associated and herpes simplex virusvectors for gene transfer. Viral vectors are currently the mostefficient and versatile method of gene transfer in target cells andtissues. Integration in the host genome is possible with the retrovirus,lentivirus, and adeno-associated virus gene transfer methods, oftenresulting in long term expression of the inserted transgene.Additionally, high transduction efficiencies have been observed in manydifferent cell types and target tissues.

The tropism of a retrovirus can be altered by incorporating foreignenvelope proteins, expanding the potential target population of targetcells. Lentiviral vectors are retroviral vector that are able totransduce or infect non-dividing cells and typically produce high viraltiters. Selection of a retroviral gene transfer system would thereforedepend on the target tissue. Retroviral vectors are comprised ofcis-acting long terminal repeats with packaging capacity for up to 6-10kb of foreign sequence. The minimum cis-acting LTRs are sufficient forreplication and packaging of the vectors, which are then used tointegrate the therapeutic gene into the target cell to provide permanenttransgene expression. Widely used retroviral vectors include those basedupon murine leukemia virus (MuLV), gibbon ape leukemia virus (GaLV),Simian Immuno deficiency virus (SIV), human immuno deficiency virus(HIV), and combinations thereof (see, e.g., Buchscher et al., J. Virol.66:2731-2739 (1992); Johann et al., J. Virol. 66:1635-1640 (1992);Sommerfelt et al., Virol. 176:58-59 (1990); Wilson et al., J. Virol.63:2374-2378 (1989); Miller et al., J. Virol. 65:2220-2224 (1991);PCT/US94/05700).

In applications where transient expression of the ZFP is preferred,adenoviral based systems are typically used. Adenoviral based vectorsare capable of very high transduction efficiency in many cell types anddo not require cell division. With such vectors, high titer and levelsof expression have been obtained. This vector can be produced in largequantities in a relatively simple system. Adeno-associated virus (“AAV”)vectors are also used to transduce cells with target nucleic acids,e.g., in the in vitro production of nucleic acids and peptides, and forin vivo and ex vivo gene therapy procedures (see, e.g., West et al.,Virology 160:38-47 (1987); U.S. Pat. No. 4,797,368; WO 93/24641; Kotin,Human Gene Therapy 5:793-801 (1994); Muzyczka, J. Clin. Invest. 94:1351(1994). Construction of recombinant AAV vectors are described in anumber of publications, including U.S. Pat. No. 5,173,414; Tratschin etal., Mol. Cell. Biol. 5:3251-3260 (1985); Tratschin, et al., Mol. Cell.Biol. 4:2072-2081 (1984); Hermonat & Muzyczka, PNAS 81:6466-6470 (1984);and Samulski et al., J. Virol. 63:03822-3828 (1989).

In particular, at least six viral vector approaches are currentlyavailable for gene transfer in clinical trials, with retroviral vectorsby far the most frequently used system. All of these viral vectorsutilize approaches that involve complementation of defective vectors bygenes inserted into helper cell lines to generate the transducing agent.

pLASN and MFG-S are examples are retroviral vectors that have been usedin clinical trials (Dunbar et al., Blood 85:3048-305 (1995); Kohn etal., Nat. Med. 1:1017-102 (1995); Malech et al., PNAS 94:22 12133-12138(1997)). PA317/pLASN was the first therapeutic vector used in a genetherapy trial. (Blaese et al., Science 270:475-480 (1995)). Transductionefficiencies of 50% or greater have been observed for MFG-S packagedvectors. (Ellem et al., Immunol Immunother. 44(1):10-20 (1997); Dranoffet al., Hum. Gene Ther. 1:111-2 (1997).

Recombinant adeno-associated virus vectors (rAAV) are a promisingalternative gene delivery systems based on the defective andnonpathogenic parvovirus adeno-associated type 2 virus. All vectors arederived from a plasmid that retains only the AAV 145 bp invertedterminal repeats flanking the transgene expression cassette. Efficientgene transfer and stable transgene delivery due to integration into thegenomes of the transduced cell are key features for this vector system.(Wagner et al., Lancet 351:9117 1702-3 (1998), Kearns et al., Gene Ther.9:748-55 (1996)).

Replication-deficient recombinant adenoviral vectors (Ad) arepredominantly used for colon cancer gene therapy, because they can beproduced at high titer and they readily infect a number of differentcell types. Most adenovirus vectors are engineered such that a transgenereplaces the Ad E1a, E1b, and E3 genes; subsequently the replicationdefector vector is propagated in human 293 cells that supply deletedgene function in trans. Ad vectors can transduce multiply types oftissues in vivo, including nondividing, differentiated cells such asthose found in the liver, kidney and muscle system tissues. ConventionalAd vectors have a large carrying capacity. An example of the use of anAd vector in a clinical trial involved polynucleotide therapy forantitumor immunization with intramuscular injection (Sterman et al.,Hum. Gene Ther. 7:1083-9 (1998)). Additional examples of the use ofadenovirus vectors for gene transfer in clinical trials includeRosenecker et al., Infection 24:1 5-10 (1996); Sterman et al., Hum. GeneTher. 9:7 1083-1089 (1998); Welsh et al., Hum. Gene Ther. 2:205-18(1995); Alvarez et al., Hum. Gene Ther. 5:597-613 (1997); Topf et al.,Gene Ther. 5:507-513 (1998); Sterman et al., Hum. Gene Ther. 7:1083-1089(1998).

Packaging cells are used to form virus particles that are capable ofinfecting a host cell. Such cells include 293 cells, which packageadenovirus, and ψ2 cells or PA317 cells, which package retrovirus. Viralvectors used in gene therapy are usually generated by producer cell linethat packages a nucleic acid vector into a viral particle. The vectorstypically contain the minimal viral sequences required for packaging andsubsequent integration into a host, other viral sequences being replacedby an expression cassette for the protein to be expressed. The missingviral functions are supplied in trans by the packaging cell line. Forexample, AAV vectors used in gene therapy typically only possess ITRsequences from the AAV genome which are required for packaging andintegration into the host genome. Viral DNA is packaged in a cell line,which contains a helper plasmid encoding the other AAV genes, namely repand cap, but lacking ITR sequences. The cell line is also infected withadenovirus as a helper. The helper virus promotes replication of the AAVvector and expression of AAV genes from the helper plasmid. The helperplasmid is not packaged in significant amounts due to a lack of ITRsequences. Contamination with adenovirus can be reduced by, e.g., heattreatment to which adenovirus is more sensitive than AAV.

In many gene therapy applications, it is desirable that the gene therapyvector be delivered with a high degree of specificity to a particulartissue type. A viral vector is typically modified to have specificityfor a given cell type by expressing a ligand as a fusion protein with aviral coat protein on the viruses outer surface. The ligand is chosen tohave affinity for a receptor known to be present on the cell type ofinterest. For example, Han et al., PNAS 92:9747-9751 (1995), reportedthat Moloney murine leukemia virus can be modified to express humanheregulin fused to gp70, and the recombinant virus infects certain humanbreast cancer cells expressing human epidermal growth factor receptor.This principle can be extended to other pairs of virus expressing aligand fusion protein and target cell expressing a receptor. Forexample, filamentous phage can be engineered to display antibodyfragments (e.g., FAB or Fv) having specific binding affinity forvirtually any chosen cellular receptor. Although the above descriptionapplies primarily to viral vectors, the same principles can be appliedto nonviral vectors. Such vectors can be engineered to contain specificuptake sequences thought to favor uptake by specific target cells.

Gene therapy vectors can be delivered in vivo by administration to anindividual patient, typically by systemic administration (e.g.,intravenous, intraperitoneal, intramuscular, subdermal, or intracranialinfusion) or topical application, as described below. Alternatively,vectors can be delivered to cells ex vivo, such as cells explanted froman individual patient (e.g., lymphocytes, bone marrow aspirates, tissuebiopsy) or universal donor hematopoietic stem cells, followed byreimplantation of the cells into a patient, usually after selection forcells which have incorporated the vector.

Ex vivo cell transfection for diagnostics, research, or for gene therapy(e.g., via re-infusion of the transfected cells into the host organism)is well known to those of skill in the art. In a preferred embodiment,cells are isolated from the subject organism, transfected with a ZFPnucleic acid (gene or cDNA), and re-infused back into the subjectorganism (e.g., patient). Various cell types suitable for ex vivotransfection are well known to those of skill in the art (see, e.g.,Freshney et al., Culture of Animal Cells, A Manual of Basic Technique(3rd ed. 1994)) and the references cited therein for a discussion of howto isolate and culture cells from patients).

In one embodiment, stem cells are used in ex vivo procedures for celltransfection and gene therapy. The advantage to using stem cells is thatthey can be differentiated into other cell types in vitro, or can beintroduced into a mammal (such as the donor of the cells) where theywill engraft in the bone marrow. Methods for differentiating CD34+ cellsin vitro into clinically important immune cell types using cytokinessuch a GM-CSF, IFN-γ and TNF-α are known (see Inaba et al., J. Exp. Med.176:1693-1702 (1992)).

Stem cells are isolated for transduction and differentiation using knownmethods. For example, stem cells are isolated from bone marrow cells bypanning the bone marrow cells with antibodies which bind unwanted cells,such as CD4+ and CD8+ (T cells), CD45+ (panB cells), GR-1(granulocytes), and Tad (differentiated antigen presenting cells) (seeInaba et al., J. Exp. Med. 176:1693-1702 (1992)).

Vectors (e.g., retroviruses, adenoviruses, liposomes, etc.) containingtherapeutic ZFP nucleic acids can be also administered directly to theorganism for transduction of cells in vivo. Alternatively, naked DNA canbe administered. Administration is by any of the routes normally usedfor introducing a molecule into ultimate contact with blood or tissuecells. Suitable methods of administering such nucleic acids areavailable and well known to those of skill in the art, and, althoughmore than one route can be used to administer a particular composition,a particular route can often provide a more immediate and more effectivereaction than another route.

Pharmaceutically acceptable carriers are determined in part by theparticular composition being administered, as well as by the particularmethod used to administer the composition. Accordingly, there is a widevariety of suitable formulations of pharmaceutical compositions of thepresent invention, as described below (see, e.g., Remington'sPharmaceutical Sciences, 17th ed., 1989).

Delivery Vehicles for ZFPs

An important factor in the administration of polypeptide compounds, suchas the ZFPs, is ensuring that the polypeptide has the ability totraverse the plasma membrane of a cell, or the membrane of anintra-cellular compartment such as the nucleus. Cellular membranes arecomposed of lipid-protein bilayers that are freely permeable to small,nonionic lipophilic compounds and are inherently impermeable to polarcompounds, macromolecules, and therapeutic or diagnostic agents.However, proteins and other compounds such as liposomes have beendescribed, which have the ability to translocate polypeptides such asZFPs across a cell membrane.

For example, “membrane translocation polypeptides” have amphiphilic orhydrophobic amino acid subsequences that have the ability to act asmembrane-translocating carriers. In one embodiment, homeodomain proteinshave the ability to translocate across cell membranes. The shortestinternalizable peptide of a homeodomain protein, Antennapedia, was foundto be the third helix of the protein, from amino acid position 43 to 58(see, e.g., Prochiantz, Current Opinion in Neurobiology 6:629-634(1996)). Another subsequence, the h (hydrophobic) domain of signalpeptides, was found to have similar cell membrane translocationcharacteristics (see, e.g., Lin et al., J. Biol. Chem. 270:1 4255-14258(1995)).

Examples of peptide sequences which can be linked to a ZFP of theinvention, for facilitating uptake of ZFP into cells, include, but arenot limited to: an 11 amino acid peptide of the tat protein of HIV; a 20residue peptide sequence which corresponds to amino acids 84-103 of thep16 protein (see Fahraeus et al., Current Biology 6:84 (1996)); thethird helix of the 60-amino acid long homeodomain of Antennapedia(Derossi et al., J. Biol. Chem. 269:10444 (1994)); the h region of asignal peptide such as the Kaposi fibroblast growth factor (K-FGF) hregion (Lin et al., supra); or the VP22 translocation domain from HSV(Elliot & O'Hare, Cell 88:223-233 (1997)). Other suitable chemicalmoieties that provide enhanced cellular uptake may also be chemicallylinked to ZFPs.

Toxin molecules also have the ability to transport polypeptides acrosscell membranes. Often, such molecules are composed of at least two parts(called “binary toxins”): a translocation or binding domain orpolypeptide and a separate toxin domain or polypeptide. Typically, thetranslocation domain or polypeptide binds to a cellular receptor, andthen the toxin is transported into the cell. Several bacterial toxins,including Clostridium perfringens iota toxin, diphtheria toxin (DT),Pseudomonas exotoxin A (PE), pertussis toxin (PT), Bacillus anthracistoxin, and pertussis adenylate cyclase (CYA), have been used in attemptsto deliver peptides to the cell cytosol as internal or amino-terminalfusions (Arora et al., J. Biol. Chem., 268:3334-3341 (1993); Perelle etal., Infect. Immun., 61:5147-5156 (1993); Stenmark et al., J. Cell Biol.113:1025-1032 (1991); Donnelly et al., PNAS 90:3530-3534 (1993);Carbonetti et al., Abstr. Annu. Meet. Am. Soc. Microbiol. 95:295 (1995);Sebo et al., Infect. Immun. 63:3851-3857 (1995); Klimpel et al., PNASU.S.A. 89:10277-10281 (1992); and Novak et al., J. Biol. Chem.267:17186-17193 1992)).

Such subsequences can be used to translocate ZFPs across a cellmembrane. ZFPs can be conveniently fused to or derivatized with suchsequences. Typically, the translocation sequence is provided as part ofa fusion protein. Optionally, a linker can be used to link the ZFP andthe translocation sequence. Any suitable linker can be used, e.g., apeptide linker.

The ZFP can also be introduced into an animal cell, preferably amammalian cell, via a liposomes and liposome derivatives such asimmunoliposomes. The term “liposome” refers to vesicles comprised of oneor more concentrically ordered lipid bilayers, which encapsulate anaqueous phase. The aqueous phase typically contains the compound to bedelivered to the cell, i.e., a ZFP.

The liposome fuses with the plasma membrane, thereby releasing the druginto the cytosol. Alternatively, the liposome is phagocytosed or takenup by the cell in a transport vesicle. Once in the endosome orphagosome, the liposome either degrades or fuses with the membrane ofthe transport vesicle and releases its contents.

In current methods of drug delivery via liposomes, the liposomeultimately becomes permeable and releases the encapsulated compound (inthis case, a ZFP) at the target tissue or cell. For systemic or tissuespecific delivery, this can be accomplished, for example, in a passivemanner wherein the liposome bilayer degrades over time through theaction of various agents in the body. Alternatively, active drug releaseinvolves using an agent to induce a permeability change in the liposomevesicle. Liposome membranes can be constructed so that they becomedestabilized when the environment becomes acidic near the liposomemembrane (see, e.g., PNAS 84:7851 (1987); Biochemistry 28:908 (1989)).When liposomes are endocytosed by a target cell, for example, theybecome destabilized and release their contents. This destabilization istermed fusogenesis. Dioleoylphosphatidylethanolamine (DOPE) is the basisof many “fusogenic” systems.

Such liposomes typically comprise a ZFP and a lipid component, e.g., aneutral and/or cationic lipid, optionally including areceptor-recognition molecule such as an antibody that binds to apredetermined cell surface receptor or ligand (e.g., an antigen). Avariety of methods are available for preparing liposomes as describedin, e.g., Szoka et al., Ann. Rev. Biophys. Bioeng. 9:467 (1980), U.S.Pat. Nos. 4,186,183, 4,217,344, 4,235,871, 4,261,975, 4,485,054,4,501,728, 4,774,085, 4,837,028, 4,235,871, 4,261,975, 4,485,054,4,501,728, 4,774,085, 4,837,028, 4,946,787, PCT Publication No. WO91\17424, Deamer & Bangham, Biochim. Biophys. Acta 443:629-634 (1976);Fraley, et al., PNAS 76:3348-3352 (1979); Hope et al., Biochim. Biophys.Acta 812:55-65 (1985); Mayer et al., Biochim. Biophys. Acta 858:161-168(1986); Williams et al., PNAS 85:242-246 (1988); Liposomes (Ostro (ed.),1983, Chapter 1); Hope et al., Chem. Phys. Lip. 40:89 (1986);Gregoriadis, Liposome Technology (1984) and Lasic, Liposomes: fromPhysics to Applications (1993)). Suitable methods include, for example,sonication, extrusion, high pressure/homogenization, microfluidization,detergent dialysis, calcium-induced fusion of small liposome vesiclesand ether-fusion methods, all of which are well known in the art.

In certain embodiments of the present invention, it is desirable totarget the liposomes of the invention using targeting moieties that arespecific to a particular cell type, tissue, and the like. Targeting ofliposomes using a variety of targeting moieties (e.g., ligands,receptors, and monoclonal antibodies) has been previously described(see, e.g., U.S. Pat. Nos. 4,957,773 and 4,603,044).

Examples of targeting moieties include monoclonal antibodies specific toantigens associated with neoplasms, such as prostate cancer specificantigen and MAGE. Tumors can also be diagnosed by detecting geneproducts resulting from the activation or over-expression of oncogenes,such as ras or c-erbB2. In addition, many tumors express antigensnormally expressed by fetal tissue, such as the alphafetoprotein (AFP)and carcinoembryonic antigen (CEA). Sites of viral infection can bediagnosed using various viral antigens such as hepatitis B core andsurface antigens (HBVc, HBVs) hepatitis C antigens, Epstein-Barr virusantigens, human immunodeficiency type-1 virus (HIV1) and papilloma virusantigens. Inflammation can be detected using molecules specificallyrecognized by surface molecules which are expressed at sites ofinflammation such as integrins (e.g., VCAM-1), selectin receptors (e.g.,ELAM-1) and the like.

Standard methods for coupling targeting agents to liposomes can be used.These methods generally involve incorporation into liposomes lipidcomponents, e.g., phosphatidylethanolamine, which can be activated forattachment of targeting agents, or derivatized lipophilic compounds,such as lipid derivatized bleomycin. Antibody targeted liposomes can beconstructed using, for instance, liposomes which incorporate protein A(see Renneisen et al., J. Biol. Chem., 265:16337-16342 (1990) andLeonetti et al., PNAS 87:2448-2451 (1990).

Doses of ZFPs

For therapeutic applications of ZFPs, the dose administered to apatient, in the context of the present invention should be sufficient toeffect a beneficial therapeutic response in the patient over time. Inaddition, particular dosage regimens can be useful for determiningphenotypic changes in an experimental setting, e.g., in functionalgenomics studies, and in cell or animal models. The dose will bedetermined by the efficacy and K_(d) of the particular ZFP employed, thenuclear volume of the target cell, and the condition of the patient, aswell as the body weight or surface area of the patient to be treated.The size of the dose also will be determined by the existence, nature,and extent of any adverse side-effects that accompany the administrationof a particular compound or vector in a particular patient.

The maximum therapeutically effective dosage of ZFP for approximately99% binding to target sites is calculated to be in the range of lessthan about 1.5×10⁵ to 1.5×10⁶ copies of the specific ZFP molecule percell. The number of ZFPs per cell for this level of binding iscalculated as follows, using the volume of a HeLa cell nucleus(approximately 1000 μm³ or 10⁻¹² L; Cell Biology, (Altman & Katz, eds.(1976)). As the HeLa nucleus is relatively large, this dosage number isrecalculated as needed using the volume of the target cell nucleus. Thiscalculation also does not take into account competition for ZFP bindingby other sites. This calculation also assumes that essentially all ofthe ZFP is localized to the nucleus. A value of 100×K_(d) is used tocalculate approximately 99% binding of to the target site, and a valueof 10×K_(d) is used to calculate approximately 90% binding of to thetarget site. For this example, K_(d)=25 nM

ZFP + target  site ↔ complexi.e., DNA + protein ↔ DNA :   protein  complex  $K_{d} = \frac{\lbrack{DNA}\rbrack \lbrack{protein}\rbrack}{\lbrack {{DNA}\text{:}\mspace{14mu} {protein}\mspace{14mu} {complex}} \rbrack}$When  50%  of  ZFP  is  bound, K_(d) = [protein]So  when  [protein] = 25  nM  and  the  nucleus  volume  is  10⁻¹²  L$\begin{matrix}{\lbrack{protein}\rbrack = {( {25 \times 10^{- 9}\mspace{14mu} {moles}\text{/}L} )( {10^{- 12}\mspace{14mu} L\text{/}{nucleus}} )}} \\{( {6 \times 10^{23}\mspace{14mu} {molecules}\text{/}{mole}} )} \\{= {15,000\mspace{14mu} {molecules}\text{/}{nucleus}\mspace{14mu} {for}\mspace{14mu} 50\% \mspace{14mu} {binding}}}\end{matrix}$When  99%  target  is  bound; 100 × K_(d) = [protein]100 × K_(d) = [protein] = 2.5  µM(2.5 × 10⁻⁶  moles/L)(10⁻¹²  L/nucleus)(6 × 10²³  molecules/mole) = about  1, 500, 000  molecules  per  nucleus   for  99%  binding  of  target  site.

The appropriate dose of an expression vector encoding a ZFP can also becalculated by taking into account the average rate of ZFP expressionfrom the promoter and the average rate of ZFP degradation in the cell.Preferably, a weak promoter such as a wild-type or mutant HSV TK isused, as described above. The dose of ZFP in micrograms is calculated bytaking into account the molecular weight of the particular ZFP beingemployed.

In determining the effective amount of the ZFP to be administered in thetreatment or prophylaxis of disease, the physician evaluates circulatingplasma levels of the ZFP or nucleic acid encoding the ZFP, potential ZFPtoxicities, progression of the disease, and the production of anti-ZFPantibodies. Administration can be accomplished via single or divideddoses.

Pharmaceutical Compositions and Administration

ZFPs and expression vectors encoding ZFPs can be administered directlyto the patient for modulation of gene expression and for therapeutic orprophylactic applications, for example, cancer, ischemia, diabeticretinopathy, macular degeneration, rheumatoid arthritis, psoriasis, HIVinfection, sickle cell anemia, Alzheimer's disease, muscular dystrophy,neurodegenerative diseases, vascular disease, cystic fibrosis, stroke,and the like. Examples of microorganisms that can be inhibited by ZFPgene therapy include pathogenic bacteria, e.g., chlamydia, rickettsialbacteria, mycobacteria, staphylococci, streptococci, pneumococci,meningococci and conococci, klebsiella, proteus, serratia, pseudomonas,legionella, diphtheria, salmonella, bacilli, cholera, tetanus, botulism,anthrax, plague, leptospirosis, and Lyme disease bacteria; infectiousfungus, e.g., Aspergillus, Candida species; protozoa such as sporozoa(e.g., Plasmodia), rhizopods (e.g., Entamoeba) and flagellates(Trypanosoma, Leishmania, Trichomonas, Giardia, etc.); viral diseases,e.g., hepatitis (A, B, or C), herpes virus (e.g., VZV, HSV-1, HSV-6,HSV-II, CMV, and EBV), HIV, Ebola, adenovirus, influenza virus,flaviviruses, echovirus, rhinovirus, coxsackie virus, cornovirus,respiratory syncytial virus, mumps virus, rotavirus, measles virus,rubella virus, parvovirus, vaccinia virus, HTLV virus, dengue virus,papillomavirus, poliovirus, rabies virus, and arboviral encephalitisvirus, etc.

Administration of therapeutically effective amounts is by any of theroutes normally used for introducing ZFP into ultimate contact with thetissue to be treated. The ZFPs are administered in any suitable manner,preferably with pharmaceutically acceptable carriers. Suitable methodsof administering such modulators are available and well known to thoseof skill in the art, and, although more than one route can be used toadminister a particular composition, a particular route can oftenprovide a more immediate and more effective reaction than another route.

Pharmaceutically acceptable carriers are determined in part by theparticular composition being administered, as well as by the particularmethod used to administer the composition. Accordingly, there is a widevariety of suitable formulations of pharmaceutical compositions of thepresent invention (see, e.g., Remington's Pharmaceutical Sciences,17^(th) ed. 1985)).

The ZFPs, alone or in combination with other suitable components, can bemade into aerosol formulations (i.e., they can be “nebulized”) to beadministered via inhalation. Aerosol formulations can be placed intopressurized acceptable propellants, such as dichlorodifluoromethane,propane, nitrogen, and the like.

Formulations suitable for parenteral administration, such as, forexample, by intravenous, intramuscular, intradermal, and subcutaneousroutes, include aqueous and non-aqueous, isotonic sterile injectionsolutions, which can contain antioxidants, buffers, bacteriostats, andsolutes that render the formulation isotonic with the blood of theintended recipient, and aqueous and non-aqueous sterile suspensions thatcan include suspending agents, solubilizers, thickening agents,stabilizers, and preservatives. In the practice of this invention,compositions can be administered, for example, by intravenous infusion,orally, topically, intraperitoneally, intravesically or intrathecally.The formulations of compounds can be presented in unit-dose ormulti-dose sealed containers, such as ampules and vials. Injectionsolutions and suspensions can be prepared from sterile powders,granules, and tablets of the kind previously described.

Regulation of Gene Expression in Plants

ZFPs can be used to engineer plants for traits such as increased diseaseresistance, modification of structural and storage polysaccharides,flavors, proteins, and fatty acids, fruit ripening, yield, color,nutritional characteristics, improved storage capability, and the like.In particular, the engineering of crop species for enhanced oilproduction, e.g., the modification of the fatty acids produced inoilseeds, is of interest.

Seed oils are composed primarily of triacylglycerols (TAGs), which areglycerol esters of fatty acids. Commercial production of these vegetableoils is accounted for primarily by six major oil crops (soybean, oilpalm, rapeseed, sunflower, cotton seed, and peanut.) Vegetable oils areused predominantly (90%) for human consumption as margarine, shortening,salad oils, and frying oil. The remaining 10% is used for non-foodapplications such as lubricants, oleochemicals, biofuels, detergents,and other industrial applications.

The desired characteristics of the oil used in each of theseapplications varies widely, particularly in terms of the chain lengthand number of double bonds present in the fatty acids making up theTAGs. These properties are manipulated by the plant in order to controlmembrane fluidity and temperature sensitivity. The same properties canbe controlled using ZFPs to produce oils with improved characteristicsfor food and industrial uses.

The primary fatty acids in the TAGs of oilseed crops are 16 to 18carbons in length and contain 0 to 3 double bonds. Palmitic acid (16:0[16 carbons:0 double bonds]), oleic acid (18:1), linoleic acid (18:2),and linolenic acid (18:3) predominate. The number of double bonds, ordegree of saturation, determines the melting temperature, reactivity,cooking performance, and health attributes of the resulting oil.

The enzyme responsible for the conversion of oleic acid (18:1) intolinoleic acid (18:2) (which is then the precursor for 18:3 formation) isΔ12-oleate desaturase, also referred to as omega-6 desaturase. A blockat this step in the fatty acid desaturation pathway should result in theaccumulation of oleic acid at the expense of polyunsaturates.

In one embodiment ZFPs are used to regulate expression of the FAD2-1gene in soybeans. Two genes encoding microsomal Δ6 desaturases have beencloned recently from soybean, and are referred to as FAD2-1 and FAD2-2(Heppard et al., Plant Physiol. 110:311-319 (1996)). FAD2-1 (delta 12desaturase) appears to control the bulk of oleic acid desaturation inthe soybean seed. ZFPs can thus be used to modulate gene expression ofFAD2-1 in plants. Specifically, ZFPs can be used to inhibit expressionof the FAD2-1 gene in soybean in order to increase the accumulation ofoleic acid (18:1) in the oil seed. Moreover, ZFPs can be used tomodulate expression of any other plant gene, such as delta-9 desaturase,delta-12 desaturases from other plants, delta-15 desaturase, acetyl-CoAcarboxylase, acyl-ACP-thioesterase, ADP-glucose pyrophosphorylase,starch synthase, cellulose synthase, sucrose synthase,senescence-associated genes, heavy metal chelators, fatty acidhydroperoxide lyase, polygalacturonase, EPSP synthase, plant viralgenes, plant fungal pathogen genes, and plant bacterial pathogen genes.

Recombinant DNA vectors suitable for transformation of plant cells arealso used to deliver the ZFP of the invention to plant cells. Techniquesfor transforming a wide variety of higher plant species are well knownand described in the technical and scientific literature (see, e.g.,Weising et al. Ann. Rev. Genet. 22:421-477 (1988)). A DNA sequencecoding for the desired ZFP is combined with transcriptional andtranslational initiation regulatory sequences which will direct thetranscription of the ZFP in the intended tissues of the transformedplant.

For example, a plant promoter fragment may be employed which will directexpression of the ZFP in all tissues of a regenerated plant. Suchpromoters are referred to herein as “constitutive” promoters and areactive under most environmental conditions and states of development orcell differentiation. Examples of constitutive promoters include thecauliflower mosaic virus (CaMV) 35S transcription initiation region, the1′- or 2′-promoter derived from T-DNA of Agrobacterium tumafaciens, andother transcription initiation regions from various plant genes known tothose of skill.

Alternatively, the plant promoter may direct expression of the ZFP in aspecific tissue or may be otherwise under more precise environmental ordevelopmental control. Such promoters are referred to here as“inducible” promoters. Examples of environmental conditions that mayeffect transcription by inducible promoters include anaerobic conditionsor the presence of light.

Examples of promoters under developmental control include promoters thatinitiate transcription only in certain tissues, such as fruit, seeds, orflowers. For example, the use of a polygalacturonase promoter can directexpression of the ZFP in the fruit, a CHS-A (chalcone synthase A frompetunia) promoter can direct expression of the ZFP in flower of a plant.

The vector comprising the ZFP sequences will typically comprise a markergene which confers a selectable phenotype on plant cells. For example,the marker may encode biocide resistance, particularly antibioticresistance, such as resistance to kanamycin, G418, bleomycin,hygromycin, or herbicide resistance, such as resistance tochlorosluforon or Basta.

Such DNA constructs may be introduced into the genome of the desiredplant host by a variety of conventional techniques. For example, the DNAconstruct may be introduced directly into the genomic DNA of the plantcell using techniques such as electroporation and microinjection ofplant cell protoplasts, or the DNA constructs can be introduced directlyto plant tissue using biolistic methods, such as DNA particlebombardment. Alternatively, the DNA constructs may be combined withsuitable T-DNA flanking regions and introduced into a conventionalAgrobacterium tumefaciens host vector. The virulence functions of theAgrobacterium tumefaciens host will direct the insertion of theconstruct and adjacent marker into the plant cell DNA when the cell isinfected by the bacteria.

Microinjection techniques are known in the art and well described in thescientific and patent literature. The introduction of DNA constructsusing polyethylene glycol precipitation is described in Paszkowski etal. EMBO J. 3:2717-2722 (1984). Electroporation techniques are describedin Fromm et al. PNAS 82:5824 (1985). Biolistic transformation techniquesare described in Klein et al. Nature 327:70-73 (1987).

Agrobacterium tumefaciens-meditated transformation techniques are welldescribed in the scientific literature (see, e.g., Horsch et al. Science233:496-498 (1984)); and Fraley et al. PNAS 80:4803 (1983)).

Transformed plant cells which are derived by any of the abovetransformation techniques can be cultured to regenerate a whole plantwhich possesses the transformed genotype and thus the desiredZFP-controlled phenotype. Such regeneration techniques rely onmanipulation of certain phytohormones in a tissue culture growth medium,typically relying on a biocide and/or herbicide marker which has beenintroduced together with the ZFP nucleotide sequences. Plantregeneration from cultured protoplasts is described in Evans et al.,Protoplasts Isolation and Culture, Handbook of Plant Cell Culture, pp.124-176 (1983); and Binding, Regeneration of Plants, Plant Protoplasts,pp. 21-73 (1985). Regeneration can also be obtained from plant callus,explants, organs, or parts thereof. Such regeneration techniques aredescribed generally in Klee et al. Ann. Rev. of Plant Phys. 38:467-486(1987).

Functional Genomics Assays

ZFPs also have use for assays to determine the phenotypic consequencesand function of gene expression. The recent advances in analyticaltechniques, coupled with focussed mass sequencing efforts have createdthe opportunity to identify and characterize many more molecular targetsthan were previously available. This new information about genes andtheir functions will speed along basic biological understanding andpresent many new targets for therapeutic intervention. In some casesanalytical tools have not kept pace with the generation of new data. Anexample is provided by recent advances in the measurement of globaldifferential gene expression. These methods, typified by gene expressionmicroarrays, differential cDNA cloning frequencies, subtractivehybridization and differential display methods, can very rapidlyidentify genes that are up or down-regulated in different tissues or inresponse to specific stimuli. Increasingly, such methods are being usedto explore biological processes such as, transformation, tumorprogression, the inflammatory response, neurological disorders etc. Onecan now very easily generate long lists of differentially expressedgenes that correlate with a given physiological phenomenon, butdemonstrating a causative relationship between an individualdifferentially expressed gene and the phenomenon is difficult. Untilnow, simple methods for assigning function to differentially expressedgenes have not kept pace with the ability to monitor differential geneexpression.

Using conventional molecular approaches, over expression of a candidategene can be accomplished by cloning a full-length cDNA, subcloning itinto a mammalian expression vector and transfecting the recombinantvector into an appropriate host cell. This approach is straightforwardbut labor intensive, particularly when the initial candidate gene isrepresented by a simple expressed sequence tag (EST). Under expressionof a candidate gene by “conventional” methods is yet more problematic.Antisense methods and methods that rely on targeted ribozymes areunreliable, succeeding for only a small fraction of the targetsselected. Gene knockout by homologous recombination works fairly well inrecombinogenic stem cells but very inefficiently in somatically derivedcell lines. In either case large clones of syngeneic genomic DNA (on theorder of 10 kb) should be isolated for recombination to workefficiently.

The ZFP technology can be used to rapidly analyze differential geneexpression studies. Engineered ZFPs can be readily used to up ordown-regulate any endogenous target gene. Very little sequenceinformation is required to create a gene-specific DNA binding domain.This makes the ZFP technology ideal for analysis of long lists of poorlycharacterized differentially expressed genes. One can simply build azinc finger-based DNA binding domain for each candidate gene, createchimeric up and down-regulating artificial transcription factors andtest the consequence of up or down-regulation on the phenotype understudy (transformation, response to a cytokine etc.) by switching thecandidate genes on or off one at a time in a model system.

This specific example of using engineered ZFPs to add functionalinformation to genomic data is merely illustrative. Any experimentalsituation that could benefit from the specific up or down-regulation ofa gene or genes could benefit from the reliability and ease of use ofengineered ZFPs.

Additionally, greater experimental control can be imparted by ZFPs thancan be achieved by more conventional methods. This is because theproduction and/or function of an engineered ZFP can be placed undersmall molecule control. Examples of this approach are provided by theTet-On system, the ecdysone-regulated system and a system incorporatinga chimeric factor including a mutant progesterone receptor. Thesesystems are all capable of indirectly imparting small molecule controlon any endogenous gene of interest or any transgene by placing thefunction and/or expression of a ZFP regulator under small moleculecontrol.

Transgenic Mice

A further application of the ZFP technology is manipulating geneexpression in transgenic animals. As with cell lines, over-expression ofan endogenous gene or the introduction of a heterologous gene to atransgenic animal, such as a transgenic mouse, is a fairlystraightforward process. The ZFP technology is an improvement in thesetypes of methods because one can circumvent the need for generatingfull-length cDNA clones of the gene under study.

Likewise, as with cell-based systems, conventional down-regulation ofgene expression in transgenic animals is plagued by technicaldifficulties. Gene knockout by homologous recombination is the methodmost commonly applied currently. This method requires a relatively longgenomic clone of the gene to be knocked out (ca. 10 kb). Typically, aselectable marker is inserted into an exon of the gene of interest toeffect the gene disruption, and a second counter-selectable markerprovided outside of the region of homology to select homologous versusnon-homologous recombinants. This construct is transfected intoembryonic stem cells and recombinants selected in culture. Recombinantstem cells are combined with very early stage embryos generatingchimeric animals. If the chimerism extends to the germline homozygousknockout animals can be isolated by back-crossing. When the technologyis successfully applied, knockout animals can be generated inapproximately one year. Unfortunately two common issues often preventthe successful application of the knockout technology; embryoniclethality and developmental compensation. Embryonic lethality resultswhen the gene to be knocked out plays an essential role in development.This can manifest itself as a lack of chimerism, lack of germlinetransmission or the inability to generate homozygous back crosses. Genescan play significantly different physiological roles during developmentversus in adult animals. Therefore, embryonic lethality is notconsidered a rationale for dismissing a gene target as a useful targetfor therapeutic intervention in adults. Embryonic lethality most oftensimply means that the gene of interest can not be easily studied inmouse models, using conventional methods.

Developmental compensation is the substitution of a related gene productfor the gene product being knocked out. Genes often exist in extensivefamilies. Selection or induction during the course of development can insome cases trigger the substitution of one family member for anothermutant member. This type of functional substitution may not be possiblein the adult animal. A typical result of developmental compensationwould be the lack of a phenotype in a knockout mouse when the ablationof that gene's function in an adult would otherwise cause aphysiological change. This is a kind of false negative result that oftenconfounds the interpretation of conventional knockout mouse models.

A few new methods have been developed to avoid embryonic lethality.These methods are typified by an approach using the cre recombinase andlox DNA recognition elements. The recognition elements are inserted intoa gene of interest using homologous recombination (as described above)and the expression of the recombinase induced in adult micepost-development. This causes the deletion of a portion of the targetgene and avoids developmental complications. The method is laborintensive and suffers form chimerism due to non-uniform induction of therecombinase.

The use of engineered ZFPs to manipulate gene expression can berestricted to adult animals using the small molecule regulated systemsdescribed in the previous section. Expression and/or function of a zincfinger-based repressor can be switched off during development andswitched on at will in the adult animals. This approach relies on theaddition of the ZFP expressing module only; homologous recombination isnot required. Because the ZFP repressors are trans dominant, there is noconcern about germline transmission or homozygosity. These issuesdramatically affect the time and labor required to go from a poorlycharacterized gene candidate (a cDNA or EST clone) to a mouse model.This ability can be used to rapidly identify and/or validate genetargets for therapeutic intervention, generate novel model systems andpermit the analysis of complex physiological phenomena (development,hematopoiesis, transformation, neural function etc.). Chimeric targetedmice can be derived according to Hogan et al., Manipulating the MouseEmbryo: A Laboratory Manual, (1988); Teratocarcinomas and Embryonic StemCells: A Practical Approach, Robertson, ed., (1987); and Capecchi etal., Science 244:1288 (1989.

All publications and patent applications cited in this specification areherein incorporated by reference as if each individual publication orpatent application were specifically and individually indicated to beincorporated by reference.

Although the foregoing invention has been described in some detail byway of illustration and example for purposes of clarity ofunderstanding, it will be readily apparent to one of ordinary skill inthe art in light of the teachings of this invention that certain changesand modifications may be made thereto without departing from the spiritor scope of the appended claims.

Examples

The following examples are provided by way of illustration only and notby way of limitation. Those of skill in the art will readily recognize avariety of noncritical parameters that could be changed or modified toyield essentially similar results.

Example I: Design and Testing of ZFPs Targeted to the Human VEGF Gene

This first Example demonstrates the construction of ZFPs designed torecognize DNA sequences contained in the promoter of the human vascularendothelial growth factor (VEGF) gene. VEGF is an approximately 46 kDaglycoprotein that is an endothelial cell-specific mitogen induced byhypoxia. VEGF has been implicated in angiogenesis associated withcancer, various retinopathies, and other serious diseases. The DNAtarget site chosen was a region surrounding the transcription initiationsite of the gene. The two 9 base pair (bp) sites chosen are found withinthe sequence agcGGGGAGGATcGCGGAGGCTtgg, where the upper-case lettersrepresent actual 9-bp targets. The protein targeting the upstream 9-bptarget was denoted VEGF1, and the protein targeting the downstream 9-bptarget was denoted VEGF3a. The major start site of transcription forVEGF is at the T at the 3′ end of the first 9-bp target, which isunderlined in the sequence above.

The human SP-1 transcription factor was used as a progenitor moleculefor the construction of designed ZFPs. SP-1 has a three fingerDNA-binding domain related to the well-studied murine Zif268 (Christy etal., PNAS 85:7857-7861 (1988)). Site-directed mutagenesis experimentsusing this domain have shown that the proposed “recognition rules” thatoperate in Zif268 can be used to adapt SP-1 to other target DNAsequences (Desjarlais & Berg, PNAS 91:11099-11103 (1994)). The SP-1sequence used for construction of zinc finger clones corresponds toamino acids 533 to 624 in the SP-1 transcription factor.

The selection of amino acids in the recognition helices of the twodesigned ZFPs, VEGF1 and VEGF3a, is summarized in Table 1.

TABLE 1 Amino acids chosen for recognition helices of VEGF-recognizingZFPs Position: Finger 1 Finger 2 Finger 3 Protein −1 2 3 6 −1 2 3 6 −1 23 6 VEGF1 T S N R R S N R R D H R VEGF3A Q S D R R S N R R D E R

Coding sequences were constructed to express these peptides using aPCR-based assembly procedure that utilizes six overlappingoligonucleotides (FIG. 1). Three oligonucleotides (oligos 1, 3, and 5 inFIG. 1) corresponding to “universal” sequences that encode portions ofthe DNA-binding domain between the recognition helices. Theseoligonucleotides remain constant for any zinc finger construct. Theother three “specific” oligonucleotides (oligos 2, 4, and 6 in FIG. 1)were designed to encode the recognition helices. These oligonucleotidescontained substitutions at positions −1, 2, 3 and 6 on the recognitionhelices to make them specific for each of the different DNA-bindingdomains. Codon bias was chosen to allow expression in both mammaliancells and E. coli.

The PCR synthesis was carried out in two steps. First, the doublestranded DNA template was created by combining the six oligonucleotides(three universal, three specific) and using a four cycle PCR reactionwith a low temperature (25°) annealing step. At this temperature, thesix oligonucleotides join to form a DNA “scaffold.” The gaps in thescaffold were filled in by a combination of Taq and Pfu polymerases. Inthe second phase of construction, the zinc finger template was amplifiedin thirty cycles by external primers that were designed to incorporaterestriction sites for cloning into pUC19. Accuracy of clones for theVEGF ZFPs were verified by DNA sequencing. The DNA sequences of each ofthe two constructs are listed below.

VEGF1:

GGTACCCATACCTGGCAAGAAGAAGCAGCACATCTGCCACATCCAGGGCTGTGGTAAAGTTTACGGCACAACCTCAAATCTGCGTCGTCACCTGCGCTGGCACACCGGCGAGAGGCCTTTCATGTGTACCTGGTCCTACTGTGGTAAACGCTTCACCCGTTCGTCAAACCTGCAGCGTCACAAGCGTACCCACACCGGTGAGAAGAAATTTGCTTGCCCGGAGTGTCCGAAGCGCTTCATGCGTAGTGACCACCTGTCCCGTCACATCAAGACCCACCAGAATAAGAAGGGTGGATCC

VEGF1 translation:

VPIPGKKKQHICHIQGCGKVYGTTSNLRRHLRWHTGERPFMCTWSYCGKRFTRSSNLQRHKRTHTGEKKFACPECPKRFMRSDHLSRHIKTHQNKKGGS

VEGF3a:

GGTACCCATACCTGGCAAGAAGAAGCAGCACATCTGCCACATCCAGGGCTGTGGTAAAGTTTACGGCCAGTCCTCCGACCTGCAGCGTCACCTGCGCTGGCACACCGGCGAGAGGCCTTTCATGTGTACCTGGTCCTACTGTGGTAAACGCTTCACCCGTTCGTCAAACCTACAGAGGCACAAGCGTACACACACCGGTGAGAAGAAATTTGCTTGCCCGGAGTGTCCGAAGCGCTTCATGCGAAGTGACGAGCTGTCACGACATATCAAGACCCACCAGAACAAGAAGGGTGGATCC

VEGF3a translation:

VPIPGKKKQHICHIQGCGKVYGQSSDLQRHLRWHTGERPFMCTWSYCGKRFTRSSNLQRHKRTHTGEKKFACPECPKRFMRSDELSRHIKTHQNKKGGS

The ability of the designed ZFPs to bind their target sites was verifiedby expressing and purifying recombinant protein from E. coli andperforming electrophoretic mobility shift assays (EMSAs). The expressionof ZFPs was carried out in two different systems. In the first, theDNA-binding peptides were expressed in E. coli by inserting them intothe commercially available pET15b vector (Novagen). This vector containsa T7 promoter sequence to drive expression of the recombinant protein.The constructs were introduced into E. coli BL21/DE3 (lacI^(q)) cells,which contain an IPTG-inducible T7 polymerase. Cultures weresupplemented with 50 μM ZnCl₂, were grown at 37° C. to an OD at 600 nmof 0.5-0.6, and protein production was induced with IPTG for 2 hrs. ZFPexpression was seen at very high levels, approximately 30% of totalcellular protein (FIG. 2). These proteins are referred to as “unfused”ZFPs.

Partially pure unfused ZFPs were produced as follows (adapted fromDesjarlais & Berg, Proteins: Structure, Function and Genetics 12:101-104(1992)). A frozen cell pellet was resuspended in 1/50th volume of 1 MNaCl, 25 mM Tris HCl (pH 8.0), 100 μM ZnCl₂, 5 mM DTT. The samples wereboiled for 10 min. and centrifuged for 10 min. at 3,000×g. At this pointthe ZFP protein in the supernatant was >50% pure as estimated bystaining of SDS polyacrylamide gels with Coomassie blue, and the productmigrated at the predicted molecular weight of around 11 kDa (FIG. 2).

The second method of producing ZFPs was to express them as fusions tothe E. coli Maltose Binding Protein (MBP). N-terminal MBP fusions to theZFPs were constructed by PCR amplification of the pET15b clones andinsertion into the vector pMal-c2 under the control of the Tac promoter(New England Biolabs). The fusion allows simple purification anddetection of the recombinant protein. It had been reported previouslythat zinc finger DNA-binding proteins can be expressed from this vectorin soluble form to high levels in E. coli and can bind efficiently tothe appropriate DNA target without refolding (Liu et al. PNAS94:5525-5530 (1997)). Production of MBP-fused proteins was as describedby the manufacturer (New England Biolabs). Transformants were grown inLB medium supplemented with glucose and ampicillin, and were inducedwith IPTG for 3 hrs at 37° C. The cells were lysed by French press, thenexposed to an agarose-based amylose resin, which specifically binds tothe MBP moiety, thus acting as an affinity resin for this protein. TheMBP fusion protein was eluted with 10 mM maltose (FIG. 2C) to releaseZFP of >50% purity. In some cases, the proteins were furtherconcentrated using a Centricon 30 filter unit (Amicon).

Partially purified unfused and MBP fusion ZFPs were tested by EMSA toassess binding to their target DNA sequences. The protein concentrationsin the preparations were measured by Bradford assay (BioRad). Since SDSpolyacrylamide gels demonstrated >50% homogeneity by either purificationmethod, no adjustment was made for ZFP purity in the calculations. Inaddition, there could be significant amounts of inactive protein in thepreparations. Therefore, the data generated by EMSAs below represent anunderestimate of the true affinity of the proteins for their targets(i.e., overestimate of K_(d)s). Two separate preparations were made foreach protein to help control for differences in ZFP activity.

The VEGF DNA target sites for the EMSA experiments were generated byembedding the 9-bp binding sites in 29-bp duplex oligonucleotides. Thesequences of the recognition (“top”) strand and their complements(“bottom”) used in the assays are as follows:

VEGF site 1, top:  5′-CATGCATAGCGGGGAGGATCGCCATCGATVEGF site 1, bottom:  5′-ATCGATGGCGATCCTCCCCGCTATGCATGVEGF site 3, top:  5′-CATGCATATCGCGGAGGCTTGGCATCGATVEGF site 3, bottom:  5′-ATCGATGCCAAGCCTCCGCGATATGCATG

The VEGF DNA target sites are underlined. The 3 bp on either side of the9 bp binding site was also derived from the actual VEGF DNA sequence.The top strand of each target site was labeled with polynucleotidekinase and γ-³²P dATP. Top and bottom strands were annealed in areaction containing each oligonucleotide at 0.5 μM, 10 mM Tris-HCl (pH8.0), 1 mM EDTA, and 50 mM NaCl. The mix was heated to 95° C. for 5 min.and slow cooled to 30° C. over 60 min. Duplex formation was confirmed bypolyacrylamide gel electrophoresis. Free label and ssDNA remaining inthe target preparations did not appear to interfere with the bindingreactions.

Binding of the ZFPs to target oligonucleotides was performed bytitrating protein against a fixed amount of duplex substrate. Twentymicroliter binding reactions contained 10 fmole (0.5 nM) 5′-³²P-labeleddouble-stranded target DNA, 35 mM Tris HCl (pH 7.8), 100 mM KCl, 1 mMMgCl₂, 1 mM dithiothreitol, 10% glycerol, 20 μg/ml poly dI-dC(optionally), 200 μg/ml bovine serum albumin, and 25 μM ZnCl₂. Proteinwas added as one fifth volume from a dilution series made in 200 mMNaCl, 20 mM Tris (pH 7.5), 1 mM DTT. Binding was allowed to proceed for30 min. at room temperature. Polyacrylamide gel electrophoresis wascarried out at 4° C. using precast 10% or 10-20% Tris-HCl gels (BioRad)and standard Tris-Glycine running buffer containing 0.1 mM ZnCl₂.

The results of a typical EMSA using an MBP fused ZFP are shown in FIG.3. In this case, a 3-fold dilution series of the MBP-VEGF1 protein wasused. The shifted product was quantitated on a phosphorimager (MolecularDynamics) and the relative signal (percent of plateau value) vs. thelog₁₀ of nM protein concentration was plotted. An apparent K_(d) wasfound by determining the protein concentration that gave half maximalbinding of MBP-VEGF1 to its target site, which in this experiment wasapproximately 2 nM.

The binding affinities determined for the VEGF proteins can besummarized as follows. VEGF1 showed the stronger DNA-binding affinity;in multiple EMSA analyses, the average apparent K_(d) was determined tobe approximately 10 nM when bound to VEGF site 1. VEGF3a bound well toits target site but with a higher apparent K_(d) than VEGF1; the averageK_(d) for VEGF3a was about 200 nM. In both cases the MBP-fused andunfused versions of the proteins bound with similar affinities. K_(d)swere also determined under these conditions for MBP fusions of thewild-type Zif268 and SP-1 ZFPs, which yielded K_(d)s of 60 and 65 nM,respectively. These results are similar to binding constants reported inthe literature for Zif268 of approximately 2-30 nM (see, e.g., Jamiesonet al., Biochemistry 33:5689-5695 (1994)). The K_(d)s for the syntheticVEGF ZFPs therefore compare very favorably with those determined forthese naturally-occurring DNA-binding proteins.

In summary, this Example demonstrates the generation of two novelDNA-binding proteins directed to specific targets near thetranscriptional start of the VEGF gene. These proteins bind withaffinities similar to those of naturally-occurring transcription factorsbinding to their targets.

Example II: Linking ZFPs to Bind an 18-Bp Target in the Human VEGF Gene

An important consideration in ZFP design is DNA target length. Forrandom DNA, a sequence of n nucleotides would be expected to occur onceevery 0.5×4^(n) base-pairs. Thus, DNA-binding domains designed torecognize only 9 bp of DNA would find sites every 130,000 bp and couldtherefore bind to multiple locations in a complex genome (on the orderof 20,000 sites in the human genome). 9-bp putative repressor-bindingsequences have been chosen for VEGF in the 5′ UTR where they mightdirectly interfere with transcription. However, in case zinc fingerdomains that recognize 9-bp sites lack the necessary affinity orspecificity when expressed inside cells, a larger domain was constructedto recognize 18 base-pairs by joining separate three-finger domains witha linker sequence to form a six-finger protein. This should ensure thatthe repressor specifically targets the appropriate sequence,particularly under conditions where only small amounts of the repressorare being produced. The 9-bp target sites in VEGF were chosen to beadjacent to one another so that the zinc fingers could be linked torecognize an 18-bp sequence. The linker DGGGS was chosen because itpermits binding of ZFPs to two 9-bp sites that are separated by a onenucleotide gap, as is the case for the VEGF1 and VEGF3a sites (see alsoLiu et al., PNAS 5525-5530 (1997)).

The 6-finger VEGF3a/1 protein encoding sequence was generated asfollows. VEGF3a was PCR amplified using the primers SPE7(5′-GAGCAGAATTCGGCAAGAAGAAGCAGCAC) and SPEamp12(5′-GTGGTCTAGACAGCTCGTCACTTCGC) to generate EcoRI and XbaI restrictionsites at the ends (restriction sites underlined). VEGF1 was PCRamplified using the primers SPEamp13 (5′-GGAGCCAAGGCTGTGGTAAAGTTTACGG)and SPEamp11 (5′-GGAGAAGCTTGGATCCTCATTATCCC) to generate StyI andHindIII restriction sites at the ends (restriction sites underlined).Using synthetic oligonucleotides, the following sequence was ligatedbetween the XbaI and StyI sites, where XbaI and StyI are underlined: TCTAGA CAC ATC AAA ACC CAC CAG AAC AAG AAA GAC GGC GGT GGC AGC GGC AAA AAGAAA CAG CAC ATA TGT CAC ATC CAA GG. This introduced the linker sequenceDGGGS between the two SP-1 domains. The ligation product was reamplifiedwith primers SPE7 and SPEamp11 and cloned into pUC19 using the EcoRI andHindIII sites. The linked ZFP sequences were then amplified with primers

(1) GB19 GCCATGCCGGTACCCATACCTGGCAAGAAGAAGCAGCAC)

(2) GB10 CAGATCGGATCCACCCTTCTTATTCTGGTGGGT to introduce KpnI and BamHIsites for cloning into the modified pMAL-c2 expression vector asdescribed above.

The nucleotide sequence of the designed, 6-finger ZFP VEGF3a/1 from KpnIto BamHI is:

GGTACCCATACCTGGCAAGAAGAAGCAGCACATCTGCCACATCCAGGGCTGTGGTAAAGTTTACGGCCAGTCCTCCGACCTGCAGCGTCACCTGCGCTGGCACACCGGCGAGAGGCCTTTCATGTGTACCTGGTCCTACTGTGGTAAACGCTTCACACGTTCGTCAAACCTACAGAGGCACAAGCGTACACACACAGGTGAGAAGAAATTTGCTTGCCCGGAGTGTCCGAAGCGCTTCATGCGAAGTGACGAGCTGTCTAGACACATCAAAACCCACCAGAACAAGAAAGACGGCGGTGGCAGCGGCAAAAAGAAACAGCACATATGTCACATCCAAGGCTGTGGTAAAGTTTACGGCACAACCTCAAATCTGCGTCGTCACCTGCGCTGGCACACCGGCGAGAGGCCTTTCATGTGTACCTGGTCCTACTGTGGTAAACGCTTCACCCGTTCGTCAAACCTGCAGCGTCACAAGCGTACCCACACCGGTGAGAAGAAATTTGCTTGCCCGGAGTGTCCGAAGCGCTTCATGCGTAGTGACCACCTGTCCCGTCACATCAAGACCCACCAGAATAAGAAGGGTGGATCC

The VEGF3a/1 amino acid translation (using single letter code) is:

VPIPGKKKQHICHIQGCGKVYGQSSDLQRHLRWHTGERPFMCTWSYCGKRFTRSSNLQRHKRTHTGEKKFACPECPKRFMRSDELSRHIKTHQNKKDGGGSGKKKQHICHIQGCGKVYGTTSNLRRHLRWHTGERPFMCTWSYCGKRFTRSSNLQRHKRTHTGEKKFACPECPKRFMRSDHLSRHIKTHQNKKGGS

The 18-bp binding protein VEGF3a/1 was expressed in E. coli as an MBPfusion, purified by affinity chromatography, and tested in EMSAexperiments as described in Example I. The target oligonucleotides wereprepared as described and comprised the following complementarysequences:

(1) JVF9 AGCGAGCGGGGAGGATCGCGGAGGCTTGGGGCAGCCGGGTAG,  and (2) JVF 10CGCTCTACCCGGCTGCCCCAAGCCTCCGCGATCCTCCCCGCT.

For the EMSA studies, 20 μl binding reactions contained 10 fmole (0.5nM) 5′-³²P-labeled double-stranded target DNA, 35 mM Tris HCl (pH 7.8),100 mM KCl, 1 mM MgCl₂, 5 mM dithiothreitol, 10% glycerol, 20 μg/ml polydI-dC, 200 μg/ml bovine serum albumin, and 25 μM ZnCl₂. Protein wasadded as one fifth volume from a 3-fold dilution series. Binding wasallowed to proceed for 60 min at either room temperature or 37° C.Polyacrylamide gel electrophoresis was carried out at room temperatureor 37° C. using precast 10% or 10-20% Tris-HCl gels (BioRad) andstandard Tris-Glycine running buffer. The room temperature assaysyielded an apparent K_(d) for this VEGF3a/1 protein of approximately 1.5nM. Thus, the 18-bp binding ZFP bound with high affinity to its targetsite. In a parallel experiment, VEGF1 protein was tested against itstarget using the oligonucleotides described in Example I, yielding anapparent K_(d) of approximately 2.5 nM. When binding and electrophoresiswere performed at 37° C., the apparent K_(d) of VEGF3a/1 wasapproximately 9 nM when tested against the 18-bp target, compared to aK_(d) of 40 nM for VEGF1 tested against its target. This indicates thatthe difference in binding affinities is accentuated at the highertemperature.

The apparent K_(d) is a useful measure of the affinity of a protein forits DNA target. However, for a DNA binding site either in vitro or invivo, its occupancy is determined to a large extent by the off-rate ofthe DNA-binding protein. This parameter can be measured by competitionexperiments as shown in FIG. 4. The conditions for EMSA were asdescribed above; binding and electrophoresis were performed at 37° C.These data indicate that the half-life of the protein-DNA complex ismore than ten times longer for VEGF3a/1 than for VEGF1. Thus, underthese in vitro conditions, the occupancy of the target site is muchhigher for the 18-bp binding protein than for the 9-bp binding protein.

Example III: Fusing Designed ZFP Sequences to Functional Domains inMammalian Expression Vectors

This Example describes the development of expression vectors forproducing ZFPs within mammalian cells, translocating them to thenucleus, and providing functional domains that are localized to thetarget DNA sequence by the ZFP. The functional domains employed are theKruppel-Associated Box (KRAB) repression domain and the Herpes SimplexVirus (HSV-1) VP16 activation domain.

Certain DNA-binding proteins contain separable domains that function astranscriptional repressors. Approximately 20% of ZFPs contain anon-DNA-binding domain of about 90 amino acids that functions as atranscriptional repressor (Thiesen, The New Biologist 2:363-374 (1990);Margolin et al., PNAS 91:4509-4513 (1994); Pengue et al., (1994), supra;Witzgall et al., (1994), supra). This domain, termed the KRAB domain, ismodular and can be joined to other DNA-binding proteins to blockexpression of genes containing the target DNA sequence (Margolin et al.,(1994); Pengue et al., (1994); Witzgall et al., (1994), supra). The KRABdomain has no effect by itself; it needs to be tethered to a DNAsequence via a DNA-binding protein to function as a repressor. The KRABdomain has been shown to block transcription initiation and can functionat a distance of up to at least 3 kb from the transcription start site.The KRAB domain from the human KOX-1 protein (Thiesen, The New Biologist2:363-37 (1990)) was used for the studies described here. This 64 aminoacid domain can be fused to ZFPs and has been shown to confer repressionin cell culture (Liu et al., supra).

The VP16 protein of HSV-1 has been studied extensively, and it has beenshown that the C-terminal 78 amino acids can act as a trans-activationdomain when fused to a DNA-binding domain (Hagmann et al., J. Virology71:5952-5962 (1997)). VP16 has also been shown to function at a distanceand in an orientation-independent manner. For these studies, amino acids413 to 490 in the VP16 protein sequence were used. DNA encoding thisdomain was PCR amplified from plasmid pMSVP16ΔC+119 using primers withthe following sequences:

(1) JVF24 CGCGGATCCGCCCCCCCGACCGATG, and (2) JVF25CCGCAAGCTTACTTGTCATCGTCGTCCTTGTAGTCGCTGCCCCCACCGTAC TCGTCAATTCC.

The downstream primer, JVF25, was designed to include a downstream FLAGepitope-encoding sequence.

Three expression vectors were constructed for these studies. The generaldesign is summarized in FIG. 5. The vectors are derived from pcDNA3.1(+)(Invitrogen), and place the ZFP constructs under the control of thecytomegalovirus (CMV) promoter. The vector carries ampicillin andneomycin markers for selection in bacteria and mammalian cell culture,respectively. A Kozak sequence for proper translation initiation (Kozak,J. Biol. Chem. 266:19867-19870 (1991)) was incorporated. To achievenuclear localization of the products, the nuclear localization sequence(NLS) from the SV40 large T antigen (Pro-Lys-Lys-Lys-Arg-Lys-Val)(Kalderon et al., Cell 39:499-509 (1984)) was added. The insertion sitefor the ZFP-encoding sequence is followed by the functional domainsequence. The three versions of this vector differ in the functionaldomain; “pcDNA-NKF” carries the KRAB repression domain sequence,“pcDNA-NVF” carries the VP16 activation domain, and “NF-control” carriesno functional domain. Following the functional domain is the FLAGepitope sequence (Kodak) to allow specific detection of the ZFPs.

The vectors were constructed as follows. Plasmid pcDNA-ΔHB wasconstructed by digesting plasmid pcDNA3.1(+) (Invitrogen) with HindIIIand BamHI, filling in the sticky ends with Klenow, and religating. Thiseliminated the HindIII, KpnI, and BamHI sites in the polylinker. Thevector pcDNA3.1(+) is described in the Invitrogen catalog. PlasmidpcDNA-NKF was generated by inserting a fragment into the EcoRI/XhoIsites of pcDNA-ΔHB that contained the following: 1) a segment from EcoRIto KpnI containing the Kozak sequence including the initiation codon andthe SV40 NLS sequence, altogether comprising the DNA sequenceGAATTCGCTAGCGCCACCATGGCCCCCAAGAAGAAGAGGAAGGTGGGAATCCAT GGGGTAC,

where the EcoRI and KpnI sites are underlined; and 2) a segment fromKpnI to XhoI containing a BamHI site, the KRAB-A box from KOX1 (aminoacid coordinates 11-53 in Thiesen, 1990, supra), the FLAG epitope (fromKodak/IBI catalog), and a HindIII site, altogether comprising thesequence GGTACCCGGGGATCCCGGACACTGGTGACCTTCAAGGATGTATTTGTGGACTTCACCAGGGAGGAGTGGAAGCTGCTGGACACTGCTCAGCAGATCGTGTACAGAAATGTGATGCTGGAGAACTATAAGAACCTGGTTTCCTTGGGCAGCGACTACAAGGACGACGATGACAAGTAAGCTTCTCGAGwhere the KpnI, BamHI and XhoI sites are underlined.

The VEGF3a/1-KRAB effector plasmid was generated by inserting aKpnI-BamHI cassette containing the ZFP sequences into pcDNA-NKF digestedwith KpnI and BamHI. The VEGF1-KRAB and VEGF3a-KRAB effector plasmidswere constructed in a similar way except that the ZFP sequences werefirst cloned into the NLS-KRAB-FLAG sequences in the context of plasmidpLitmus 28 (New England Biolabs) and subsequently moved to theBamHI-XhoI sites of pcDNA3.1(+) as a BglII-XhoI cassette, where theBglII site was placed immediately upstream of the EcoRI site (seeExample IV for expression of these vectors).

The effector plasmids used in Example V were constructed as follows.Plasmid pcDNA-NVF was constructed by PCR amplifying the VP16transactivation domain, as described above, and inserting the productinto the BamHI/HindIII sites of pcDNA-NKF, replacing the KRAB sequence.The sequence of the inserted fragment, from BamHI to HindIII, was:

GGATCCGCCCCCCCGACCGATGTCAGCCTGGGGGACGAGCTCCACTTAGACGGCGAGGACGTGGCGATGGCGCATGCCGACGCGCTAGACGATTTCGATCTGGACATGTTGGGGGACGGGGATTCCCCGGGGCCGGGATTTACCCCCCACGACTCCGCCCCCTACGGCGCTCTGGATATGGCCGACTTCGAGTTTGAGCAGATGTTTACCGATGCCCTTGGAATTGACGAGTACGGTGGGGGCAGCGACTACAAGGACGACGATGACAAGTAAGCTT.

VEGF1-VP16 and VEGF3a/1-VP16 vectors were constructed by inserting aKpnI-BamHI cassette containing the ZFP sequences into pcDNA-NVF digestedwith KpnI and BamHI.

The effector plasmids used in Example VI were constructed as follows.

Plasmid NF-control was generated by inserting the sequenceGAATTCGCTAGCGCCACCATGGCCCCCAAGAAGAAGAGGAAGGTGGGAATCCATGGGGTACCCGGGGATGGATCCGGCAGCGACTACAAGGACGACGATGACAAGTA AGCTTCTCGAG

into the EcoRI-XhoI sites of pcDNA-NKF, thereby replacing theNLS-KRAB-FLAG sequences with NLS-FLAG only.

VEGF1-NF and VEGF3a/1-NF were constructed by inserting a KpnI-BamHIcassette containing the ZFP sequences into NF-control digested with KpnIand BamHI. CCR5-KRAB was constructed in the same way as the VEGF KRABvectors, except that the ZFP sequences were designed to be specific fora DNA target site that is unrelated to the VEGF targets.

Finally, control versions of both the KRAB and VP16 expression plasmidswere constructed. Plasmid NKF-control was designed to expressNLS-KRAB-FLAG without zinc finger protein sequences; plasmid NVF-controlwas designed to express NLS-VP16-FLAG without ZFP sequences. Theseplasmids were made by digesting pcDNA-NKF and -NVF, respectively, withBamHI, filling in the ends with Klenow, and religating in order to placethe downstream domains into the proper reading frame. These plasmidsserve as rigorous controls for cell culture studies.

Mammalian cell expression and nuclear localization of the VEGFengineered ZFPs was demonstrated through immunofluorescence studies. 293(human embryonic kidney) cells were transfected with the expressionplasmid encoding the NLS-VEGF1-KRAB-FLAG chimera. Lipofectamine was usedas described below. After 24-48 hours, cells were fixed and exposed to aprimary antibody against the FLAG epitope. A secondary antibody labeledwith Texas Red was applied, and the cells were counter stained withDAPI. Texas Red staining was observed to consistently co-localize withthe DAPI staining, indicating that the ZFP being expressed from thisplasmid was nuclear localized.

Example IV: Repression of VEGF Reporters in Co-Transfection Experiments

This Example demonstrates the use of transient co-transfection studiesto measure the activity of the ZFP repressor proteins in cells. Suchexperiments involve co-transfection of ZFP-KRAB expression (“effector”)plasmids with reporter plasmids carrying the VEGF target sites. Efficacyis assessed by the repression of reporter gene expression in thepresence of the effector plasmid relative to empty vector controls.

The reporter plasmid system was based on the pGL3 firefly luciferasevectors (Promega). Four copies of the VEGF target sites were insertedupstream of the SV40 promoter, which is driving the firefly luciferasegene, in the plasmid pGL3-Control to create pVFR1-4x. This plasmidcontains the SV40 enhancer and expresses firefly luciferase to highlevels in many cell types. Insertions were made by ligating togethertandem copies of the two complementary 42-bp oligonucleotides, JVF9 andJVF10, described in Example II. Adaptor sequences were ligated on, andthe assembly was inserted into the MluI/BglII sites of pGL3-Control.This resulted in the insertion of the following sequence between thosesites:

ACGCGTaagcttGCTAGCGAGCGGGGAGGATCGCGGAGGCTTGGGGCAGCCGGGTAGAGCGAGCGGGGAGGATCGCGGAGGCTTGGGGCAGCCGGGTAGAGCGAGCGGGGAGGATCGCGGAGGCTTGGGGCAGCCGGGTAGAGCGAGCGGGGAGGATCGCGGAGGCTTGGGGCAGCCGGGTAGAGCGCTCAGaagcttAG ATCT.

The first six and last six nucleotides shown are the MluI and BglIIsites; the lowercase letters indicate HindIII sites. The binding sitesfor VEGF1 and VEGF3a are underlined.

The effector plasmid construction is described above. The VEGF1-KRAB,VEGF3a-KRAB, and VEGF3a/1-KRAB expression vectors were designed toproduce a fusion of the SV40 nuclear localization sequence, the VEGFZFP, the KRAB repression domain, and a FLAG epitope marker all under thecontrol of the CMV promoter. The empty pcDNA3.1 expression vector wasused as a control (pcDNA).

All vectors were prepared using Qiagen DNA purification kits. FIG. 6shows a typical set of transfections using COS-1 (African green monkeykidney) cells. Approximately 40,000 cells were seeded into each well ofa 24-well plate and allowed to grow overnight in Dulbecco's ModifiedEagle Medium (D-MEM) medium containing 10% fetal bovine serum at 37° C.with 5% CO₂. Cells were washed with PBS and overlayed with 200 μl ofserum-free D-MEM. Plasmids were introduced using lipofectamine(Gibco-BRL). Each well was transfected with about 0.3 μg of effectorplasmid, 0.3 μg of reporter plasmid, and 0.01 μg of plasmid pRL-SV40(Promega) that had been complexed with 6 μl of lipofectamine and 25 μlof D-MEM for 30 min at 37° C. Transfections were done in triplicate.After 3 hrs, 1 ml of medium containing 10% serum was added to each well.Cells were harvested 40-48 hours after transfection. Luciferase assayswere done using the Dual Luciferase™ System (Promega). The third plasmidtransfected, pRL-SV40, carries the Renilla luciferase gene and wasco-transfected as a standard for transfection efficiency. The data shownin FIG. 6 are the averages of triplicate assays normalized against theRenilla activity.

For the control reporter plasmid pGL3-Control (pGL3-C), the presence orabsence of the ZFP-KRAB expression plasmid does not influence theluciferase expression level. However, for pVFR1-4x, the reportercontaining four copies of the VEGF target site, presence of the VEGF1(9-bp-binding ZFP) or VEGF3a/1 (18-bp-binding ZFP) expression plasmidreduces luciferase expression by a factor of 2-3 relative to the emptypcDNA vector control. The VEGF3a (9-bp-binding ZFP) expression plasmidappears to exhibit little or no effect. These experiments clearlydemonstrate that a designed ZFP is capable of functioning in a cell torepress transcription of a gene when its target site is present.Furthermore, it appears that a certain level of affinity is required forfunction; i.e., VEGF1 and VEGF3a/1, with K_(d)s of 10 nM or less, arefunctional, whereas VEGF3a, with a K_(d) of 200 nM, is not.

A second reporter plasmid, pVFR2-4x, was constructed by removing thefour copies of the VEGF target sites using HindIII and inserted theminto the HindIII site of pGL3-Control (in the forward orientation). Thisplaces the target sites between the start site of transcription for theSV40 promoter and the translational start codon of the luciferase gene.In similar co-transfection experiments to those described, approximately3-4 fold repression of the luciferase signal was observed with theVEGF1-KRAB or VEGF3a/1-KRAB repressors relative to the pcDNA controls(data not shown). This indicates that the repressors are active whenbound either upstream or downstream of the start of transcription.

Example V: Activation of VEGF Reporters in Co-Transfection Experiments

This Example demonstrates the use of transient co-transfection studiesto measure the activity of the ZFP transcriptional activators in cells.The experimental setup is similar to that of Example IV except that adifferent transfection method, a different cell line, and a differentset of reporter and effector plasmids was used.

For activation experiments, a reporter was constructed labeled pVFR3-4x.This reporter contains the four copies of the VEGF targets, with thesequence shown above, at the MluI/BglII sites of plasmid pGL3-Promoter(Promega). This vector has been deleted for the SV40 enhancer sequenceand therefore has a lower basal level of firefly luciferase expression.pVFR3-4x was constructed by swapping the KpnI/NcoI fragment of pVFR1-4xinto the KpnI/NcoI sites of pGL3-Promoter.

The effector plasmid construction is described above. The VEGF1-VP16,VEGF3a-VP16, and VEGF3a/1-VP16 expression vectors were designed toproduce a fusion of the SV40 nuclear localization sequence, the VEGFZFP, the VP16 trans-activation domain, and a FLAG epitope tag all underthe control of the CMV promoter. The empty pcDNA3 expression vector wasused as a control.

All vectors were prepared using Qiagen DNA purification kits. FIG. 7shows a typical set of transfections using 293 (human embryonic kidney)cells. Approximately 40,000 cells were seeded into each well of a24-well plate and allowed to grow overnight in D-MEM medium containing10% fetal bovine serum at 37° C. with 5% CO₂. Cells were washed withserum-free D-MEM and overlayed with 200 μl of the same. Plasmids wereintroduced using a calcium phosphate transfection kit (Gibco-BRL)according to the manufacturer's instructions. Cells in each well weretransfected with 1.5 μg of reporter plasmid, 1.5 μg of effector plasmid,and 0.5 μg of an actin/β-gal plasmid. Plasmids were combined with 15 μlof CaCl₂ and brought to 100 μl with dH₂O. 100 μl of HEPES solution wasadded dropwise while vortexing. The mix was incubated for 30 min at roomtemperature. The 200 μl of calcium phosphate-treated DNA was then addedto the medium in each well. Transfections were done in triplicate. After5 hours, the medium was removed and 1 ml of medium containing 10% serumwas added. Cells were harvested 40-48 hours after transfection.Luciferase assays were done using the Dual-Light™ system (Tropix). Thethird plasmid transfected, actin/β-gal, carries the β-galactosidase geneunder the control of the actin promoter and was co-transfected as astandard for transfection efficiency. The β-galactosidase assays werealso done according to the manufacturer's protocol (Tropix). The datashown in FIG. 7 are the average of triplicate assays normalized againstthe β-galactosidase activity.

For the control reporter plasmid, pGL3-Promoter (pGL3-P), the presenceor absence of the ZFP-VP16 expression plasmid does not significantlyinfluence the luciferase expression level. For pVFR3-4x, the reportercontaining four copies of the VEGF target site, presence of VEGF1 (the9-bp-binding ZFP) shows a very slight activation relative to the emptypcDNA vector control. VEGF3a/1 (the 18-bp-binding ZFP) expressionplasmid activates luciferase expression very substantially, showingabout a 14-fold increase relative to pcDNA. These experiments clearlydemonstrate that a designed ZFP, when fused to the VP16 activationdomain, is capable of functioning in a cell to activate transcription ofa gene when its target site is present. Furthermore, these resultsclearly demonstrate that an 18-bp binding protein, VEGF3a/1, is a muchbetter activator in this assay than a 9-bp binding VEGF1 protein. Thiscould be a result of the improved affinity or decreased off-rate of theVEGF3a/1 protein.

A fourth VEGF reporter plasmid was constructed by cloning the KpnI/NcoIfragment of pVFR2-4x into pGL3-Promoter to create plasmid pVFR4-4x.Activation was observed in co-transfections using this reporter incombination with effector plasmids expressing the VEGF1-VP16 andVEGF3a/1-VP16 fusions (data not shown). This indicates that theseartificial trans-activators are functional when bound either upstream ordownstream of the start of transcription.

These co-transfection data demonstrate that ZFPs can be used to regulateexpression of reporter genes. Such experiments serve as a useful toolfor identifying ZFPs for further use as modulators of expression ofendogenous cellular genes. As is shown below, modulation results canvary between co-transfection experiments and endogenous geneexperiments, while using the same ZFP construct.

Example VI: Repression of an Endogenous VEGF Gene in Human Cells

This Example demonstrates that a designed ZFP can repress expression ofan endogenous cellular gene that is in its natural context and chromatinstructure. Specifically, effector plasmids expressing VEGF ZFPs fused tothe KRAB repression domain were introduced into cells and were shown todown-regulate the VEGF gene.

Eucaryotic expression vectors were constructed that fuse the VEGF3a/1and the VEGF1 ZFPs to the SV40 NLS and KRAB, as described above inExample III. Transfections were done using Lipofectamine, a commerciallyavailable liposome preparation from GIBCO-BRL. All plasmid DNAs wereprepared using Qiagen Midi DNA purification system. 10 μg of theeffector plasmid was mixed with 100 μg of Lipofectamine (50 μl) in atotal volume of 1600 μl of Opti-MEM. A pCMVβ-gal plasmid (Promega) wasalso included in the DNA mixture as an internal control for transfectionefficiency. Following a 30 minute incubation, 6.4 ml of DMEM was addedand the mixture was layered on 3×10⁶ 293 cells. After five hours, theDNA-Lipofectamine mixture was removed, and fresh culture mediumcontaining 10% fetal bovine serum was layered on the cells.

Eighteen hours post transfection, the 293 cells were induced bytreatment with 100 μM DFX (desferrioxamine), resulting in a rapid andlasting transcriptional activation of the VEGF gene and also in agradual increase in VEGF mRNA stability (Ikeda et al., J. Biol. Chem.270:19761-19766 (1995)). Under routine culture conditions, 293 cellssecrete a low level of VEGF in the culture media. The cells were allowedto incubate an additional 24 hours before the supernatants werecollected for determination of VEGF levels by an ELISA assay.

In parallel experiments that demonstrated a similar level of repression,cell viability was monitored using the Promega Celltiter 96® Aqueous OneSolution cell proliferation assay (Promega). After Dfx treatment for 18hours, 500 μL of the original 2 ml of media was removed and analyzed forVEGF expression, as described above. To evaluation cell viability, 300μL of Promega Celltiter 96® Aqueous One Solution Reagent was added tothe remaining 1.5 ml. The cells were then incubated at 37° C. forapproximately 2 hours. 100 μL from each well was transferred to a96-well plate and read on an ELISA plate reader at OD 490 nm. There wasno significant reduction in viability of cells expressing theVEGF3a/1-KRAB construct relative to those transfected with empty vectorcontrols, indicating that the VEGF repression observed was not due togeneralized cell death.

A 40-50-fold decrease in VEGF expression was noted in the DFX treatedcells transfected with VEGF3a/1-KRAB, an expression vector encoding the18 bp binding VEGF high affinity ZFP. A two-fold decrease in expressionwas observed when cells were transfected with VEGF1-KRAB, an expressionvector encoding the 9 bp binding VEGF high affinity ZFP. No significantdecrease in VEGF expression was observed in cells that were transfectedwith a non-VEGF ZFP (CCR5-KRAB) or NKF-control (FIG. 8). Similar resultshave been obtained in three independent transfection experiments.

In a separate experiment, the following results were obtained (data notshown). VEGF1-NF, which expresses the 9-bp-binding VEGF1 ZFP without afunctional domain, showed no effect on VEGF gene expression. Asignificant reduction in VEGF expression was observed with VEGF3a/1-NF,which expresses the 18-bp binding protein without a functional domain.This result suggests that binding to the start site of transcription,even without a repression domain, interferes with transcription. Evenwhen fused to the KRAB domain, the VEGF3a ZFP is unable to affectexpression levels (plasmid VEGF3a-KRAB). However, VEGF1 fused to KRAB(VEGF1-KRAB) results in a dramatic decrease in expression. VEGF3a/1fused to KRAB (VEGF3a/1-KRAB) prevents expression of VEGF altogether.

These data indicate that a designed ZFP is capable of locating andbinding to its target site on the chromosome and preventing expressionof an endogenous cellular target gene. In particular, the resultsindicate that ZFPs with a K_(d) of less than about 25 nM (e.g., VEGF1has an average apparent K_(d) of about 10 nM) provide dramatic decreasesin expression. In addition, the data demonstrate that the KRABfunctional domain enhances gene silencing. Because in this experimentthe introduction of the repressor occurs before the inducer of VEGF isadded (DFX), the data demonstrate the ability of a designed repressor toprevent activation of an already quiescent gene. In addition, theseresults demonstrate that a six-finger engineered ZFP (VEGF3a/1) withnanomolar affinity for its target is able to inhibit the hypoxicresponse of the VEGF gene when it binds a target that overlaps thetranscriptional start site.

Example VII: Activation of Endogenous VEGF Gene in Human Cells

This Example demonstrates that a designed ZFP can activate theexpression of a gene that is in its natural context and chromatinstructure. Specifically, effector plasmids expressing VEGF ZFPs fused tothe VP16 activation domain were introduced into cells and were shown toup-regulate the VEGF gene.

Eucaryotic expression vectors were constructed that fuse the VEGF3a/1and the VEGF1 ZFPs to the SV40 NLS and VP16, as described in ExampleIII. Transfections were done using Lipofectamine, a commerciallyavailable liposome preparation from GIBCO-BRL. All plasmid DNAs wereprepared using the Qiagen Midi DNA purification system. 10 μg of theeffector plasmid (containing the engineered ZFP) was mixed with 100 μgof Lipofectamine (50 μl) in a total volume of 1600 μl of Opti-MEM. ApCMVβ-gal plasmid (Promega) was also included in the DNA mixture as aninternal control for transfection efficiency. Following a 30 minuteincubation, 6.4 ml of DMEM was added and the mixture was layered on3×10⁶ 293 cells. After five hours, the DNA-Lipofectamine mixture wasremoved, and fresh culture medium containing 10% fetal bovine serum waslayered on the cells. One day later, fresh media was added and thesupernatant was collected 24 hours later for determination of VEGFlevels using a commercially available ELISA kit (R and D Systems).

For the three-fingered VEGF1-specific ZFP (VEGF1-VP16), a 7-10 foldincrease in VEGF expression was observed when compared to controlplasmid (NVF-control) and mock transfected cells (FIG. 9). Similarresults have been obtained in 5 independent experiments. It is importantto note that the level of VEGF secretion in VEGF1-VP16 transfected cellswas equivalent or greater than the level in cells that have been treatedwith DFX (FIG. 9). Introduction of VEGF3a/1-VP16 stimulated a moremodest induction of VEGF. This result is consistent with the finding inExample VI, in which expression of the 18-bp binding protein without afunctional domain prevented activation to a certain degree. This resultsuggested that the tight binding of this protein to the start site oftranscription interferes with activation.

These data indicate that a designed ZFP is capable of locating andbinding to its target site on the chromosome, presenting atranscriptional activation domain, and dramatically enhancing theexpression level of that gene. In particular, the results indicate thatZFPs with a K_(d) of less than about 25 nM (e.g., VEGF1 has an averageapparent K_(d) of about 10 nM) provide dramatic increases in expression.

Example VIII: RNase Protection Assay

To further substantiate the results in Examples VI and VII, aribonuclease protection assay (RPA) was performed to correlate theincreased level of VEGF protein with an increase in VEGF mRNA levels(Example VII), and to correlate the decreased level of VEGF protein witha decrease in VEGF mRNA levels (Example VI).

RNA was isolated from the transfected cells using an RNA isolation kit(Pharmingen). Radiolabeled multi template probes, which included a VEGFspecific probe, were prepared by in vitro transcription and hybridizedovernight at 56° C. to 5 μg of each of the RNAs from the experimentaland control transfected cells. The hybridization mixture was treatedwith RNase and the protected probes were purified and subjected to 5%denaturing polyacrylamide gel electrophoresis and the radioactivity wasevaluated by autoradiography. 293 cells transfected with the VEGF1-VP16had a 2-4 fold increase in the level of VEGF mRNA when compared to cellstransfected with NVF-control (FIG. 10A; see Example VII for experimentaldetails). The size of the protected probe was identical to the size ofthe probe generated from the control human RNA provided as a control forRNA integrity. (FIG. 10A).

In a separate experiment, the level of VEGF specific mRNA was alsoquantitated in cells that had been transfected with a VEGF-KRAB effectorplasmid (FIG. 10B; see Example VI for experimental details). The detailsof the transfection are described in Example VI. A dramatic decrease inthe level of VEGF mRNA was observed when cells were transfected with theVEGF3a/1-KRAB effector plasmid. No significant decrease in VEGF mRNA wasobserved when cells were transfected with NKF-control or a non-VEGFspecific ZFP (CCR5-5-KRAB and CCR5-3-KRAB, which recognize differentCCR5 target sites).

This experiment demonstrates that the increase in VEGF protein observedupon transfection with the VEGF1-VP16 chimeric transcription factor ismediated by an increase in the level of VEGF mRNA. Similarly, thedecrease in VEGF protein observed upon transfection with theVEGF3a/1-KRAB chimeric transcription factor is mediated by a decrease inthe level of VEGF mRNA.

What is claimed is:
 1. A method of modulating expression of anendogenous cellular gene in a cell, the method comprising the steps of:administering to the cell a nucleic acid molecule comprising apolynucleotide sequence which encodes a fusion molecule, the fusionmolecule comprising an engineered DNA-binding domain and a regulatorydomain, wherein the nucleic acid molecule expresses the fusion proteinin the cell, thereby modulating expression of the endogenous cellulargene.
 2. The method of claim 1, wherein the fusion protein comprises atleast two regulatory domains.
 3. The method of claim 1, wherein the cellis selected from the group consisting of animal cell, a plant cell, abacterial cell, a protozoal cell, or a fungal cell.
 4. The method ofclaim 3, wherein the cell is a mammalian cell.
 5. The method of claim 3,wherein the cell is a human cell.
 6. The method of claim 1, wherein theregulatory domain is selected from the group consisting of atranscriptional repressor, a transcriptional activator, an endonuclease,a methyl transferase, and a histone deacetylase.
 7. The method of claim1, wherein the step of administering the nucleic acid molecule to thecell comprises administering the nucleic acid molecule in alipid:nucleic acid complex or as naked nucleic acid.
 8. The method ofclaim 1, wherein the nucleic acid molecule is an expression vectorcomprising the fusion protein-encoding nucleic acid operably linked to apromoter.
 9. The method of claim 8, wherein the expression vector is aviral expression vector.
 10. The method of claim 8, wherein theexpression vector is a retroviral expression vector, an adenoviralexpression vector, or an AAV expression vector.
 11. The method of claim8, wherein the promoter is an inducible promoter.
 12. The method ofclaim 1, wherein the target site is upstream of a transcriptioninitiation site of the endogenous cellular gene.
 13. The method of claim1, wherein the target site is adjacent to a transcription initiationsite of the endogenous cellular gene.
 14. The method of claim 1, whereinthe target site is adjacent to an RNA polymerase pause site, wherein theRNA polymerase pause site is downstream of a transcription initiationsite of the endogenous cellular gene.